v3.26.1
Shareholder Report
 12 Months Ended
Apr. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSR
Amendment Flag false
Registrant Name MFS SERIES TRUST IX
Entity Central Index Key 0000063075
Entity Investment Company Type N-1A
Document Period End Date Apr. 30, 2026
C000006757 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Municipal LimitedMaturity Fund
Class Name Class A
Trading Symbol MTLFX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Municipal Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
A $59 0.58%
Expenses Paid, Amount $ 59
Expense Ratio, Percent 0.58%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class A shares of the MFS Municipal Limited Maturity Fund (fund) provided a total return of 4.95%, at net asset value. This compares with a return of 6.34% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg 1-9 Year Municipal Bond Index, generated a return of 4.91%.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • The municipal market produced positive returns over the trailing year, characterized by a supportive backdrop punctuated by bouts of volatility. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year, providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. Volatility rose again in March of this year due to heightened geopolitical risks and related economic effects before returning to relatively low levels late in the period. Resilient inflows and generally solid credit fundamentals were key supports for the asset class. The benchmark index for this fund generated a return of 4.91% for the period. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.03%, higher than the five-year average of 2.60%.
  • Top contributors to performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund’s overweight to the housing sector and underweight to general obligation bonds aided relative performance. Favorable security selection within both the transportation and education sectors also supported relative results.
    • From a quality perspective, an overweight to BBB-rated and below investment grade bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund's overweight to the 10 to 20-year segment of the yield curve detracted from relative returns as yields in that segment declined less than bonds with shorter maturities.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. This graph includes the deduction of the maximum applicable sales charge.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
A without sales charge 4.95% 1.49% 1.94%
A with initial sales charge (2.50%) 2.33% 0.98% 1.69%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆ 6.34% 0.90% 2.20%
Bloomberg 1-9 Year Municipal Bond Index ∆ 4.91% 1.27% 1.81%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/a for more recent performance information.
Net Assets $ 3,116,903,553
Holdings Count | Holding 1,069
Advisory Fees Paid, Amount $ 9,561,990 [1]
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,116,903,553 Average Effective Maturity (yrs): 5.2
Total Number of Holdings: 1,069 Average Effective Duration (yrs): 3.7
Total Management Fee ($)#: 9,561,990
Portfolio Turnover Rate (%): 26
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 96.4%
Money Market Funds 3.6%
Composition including fixed income credit
quality
AAA 2.7%
AA 34.4%
A 37.0%
BBB 13.6%
BB 3.5%
B 0.3%
Not Rated 4.9%
Money Market Funds 3.6%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006758 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Municipal LimitedMaturity Fund
Class Name Class B
Trading Symbol MTLBX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Municipal Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
B $136 1.33%
Expenses Paid, Amount $ 136
Expense Ratio, Percent 1.33%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class B shares of the MFS Municipal Limited Maturity Fund (fund) provided a total return of 4.04%, at net asset value. This compares with a return of 6.34% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg 1-9 Year Municipal Bond Index, generated a return of 4.91%.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • The municipal market produced positive returns over the trailing year, characterized by a supportive backdrop punctuated by bouts of volatility. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year, providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. Volatility rose again in March of this year due to heightened geopolitical risks and related economic effects before returning to relatively low levels late in the period. Resilient inflows and generally solid credit fundamentals were key supports for the asset class. The benchmark index for this fund generated a return of 4.91% for the period. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.03%, higher than the five-year average of 2.60%.
  • Top contributors to performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund’s overweight to the housing sector and underweight to general obligation bonds aided relative performance. Favorable security selection within both the transportation and education sectors also supported relative results.
    • From a quality perspective, an overweight to BBB-rated and below investment grade bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund's overweight to the 10 to 20-year segment of the yield curve detracted from relative returns as yields in that segment declined less than bonds with shorter maturities.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
B without sales charge 4.04% 0.74% 1.19%
B with CDSC (declining over six years from 4% to 0%)× 0.04% 0.36% 1.19%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆ 6.34% 0.90% 2.20%
Bloomberg 1-9 Year Municipal Bond Index ∆ 4.91% 1.27% 1.81%
∆
Source: FactSet Research Systems Inc.
×
Assuming redemption at the end of the applicable period.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/b for more recent performance information.
Net Assets $ 3,116,903,553
Holdings Count | Holding 1,069
Advisory Fees Paid, Amount $ 9,561,990 [2]
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,116,903,553 Average Effective Maturity (yrs): 5.2
Total Number of Holdings: 1,069 Average Effective Duration (yrs): 3.7
Total Management Fee ($)#: 9,561,990
Portfolio Turnover Rate (%): 26
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 96.4%
Money Market Funds 3.6%
Composition including fixed income credit
quality
AAA 2.7%
AA 34.4%
A 37.0%
BBB 13.6%
BB 3.5%
B 0.3%
Not Rated 4.9%
Money Market Funds 3.6%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006759 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Municipal LimitedMaturity Fund
Class Name Class C
Trading Symbol MTLCX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Municipal Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
C $146 1.43%
Expenses Paid, Amount $ 146
Expense Ratio, Percent 1.43%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class C shares of the MFS Municipal Limited Maturity Fund (fund) provided a total return of 3.94%, at net asset value. This compares with a return of 6.34% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg 1-9 Year Municipal Bond Index, generated a return of 4.91%.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • The municipal market produced positive returns over the trailing year, characterized by a supportive backdrop punctuated by bouts of volatility. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year, providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. Volatility rose again in March of this year due to heightened geopolitical risks and related economic effects before returning to relatively low levels late in the period. Resilient inflows and generally solid credit fundamentals were key supports for the asset class. The benchmark index for this fund generated a return of 4.91% for the period. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.03%, higher than the five-year average of 2.60%.
  • Top contributors to performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund’s overweight to the housing sector and underweight to general obligation bonds aided relative performance. Favorable security selection within both the transportation and education sectors also supported relative results.
    • From a quality perspective, an overweight to BBB-rated and below investment grade bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund's overweight to the 10 to 20-year segment of the yield curve detracted from relative returns as yields in that segment declined less than bonds with shorter maturities.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
C without sales charge 3.94% 0.61% 1.07%
C with CDSC (1% for 12 months)× 2.94% 0.61% 1.07%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆ 6.34% 0.90% 2.20%
Bloomberg 1-9 Year Municipal Bond Index ∆ 4.91% 1.27% 1.81%
∆
Source: FactSet Research Systems Inc.
×
Assuming redemption at the end of the applicable period.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/c for more recent performance information.
Net Assets $ 3,116,903,553
Holdings Count | Holding 1,069
Advisory Fees Paid, Amount $ 9,561,990 [3]
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,116,903,553 Average Effective Maturity (yrs): 5.2
Total Number of Holdings: 1,069 Average Effective Duration (yrs): 3.7
Total Management Fee ($)#: 9,561,990
Portfolio Turnover Rate (%): 26
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 96.4%
Money Market Funds 3.6%
Composition including fixed income credit quality
AAA 2.7%
AA 34.4%
A 37.0%
BBB 13.6%
BB 3.5%
B 0.3%
Not Rated 4.9%
Money Market Funds 3.6%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000092113 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Municipal LimitedMaturity Fund
Class Name Class I
Trading Symbol MTLIX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Municipal Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
I $44 0.43%
Expenses Paid, Amount $ 44
Expense Ratio, Percent 0.43%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class I shares of the MFS Municipal Limited Maturity Fund (fund) provided a total return of 4.98%, at net asset value. This compares with a return of 6.34% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg 1-9 Year Municipal Bond Index, generated a return of 4.91%.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • The municipal market produced positive returns over the trailing year, characterized by a supportive backdrop punctuated by bouts of volatility. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year, providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. Volatility rose again in March of this year due to heightened geopolitical risks and related economic effects before returning to relatively low levels late in the period. Resilient inflows and generally solid credit fundamentals were key supports for the asset class. The benchmark index for this fund generated a return of 4.91% for the period. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.03%, higher than the five-year average of 2.60%.
  • Top contributors to performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund’s overweight to the housing sector and underweight to general obligation bonds aided relative performance. Favorable security selection within both the transportation and education sectors also supported relative results.
    • From a quality perspective, an overweight to BBB-rated and below investment grade bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund's overweight to the 10 to 20-year segment of the yield curve detracted from relative returns as yields in that segment declined less than bonds with shorter maturities.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
I without sales charge 4.98% 1.61% 2.09%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆ 6.34% 0.90% 2.20%
Bloomberg 1-9 Year Municipal Bond Index ∆ 4.91% 1.27% 1.81%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/i for more recent performance information.
Net Assets $ 3,116,903,553
Holdings Count | Holding 1,069
Advisory Fees Paid, Amount $ 9,561,990 [4]
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,116,903,553 Average Effective Maturity (yrs): 5.2
Total Number of Holdings: 1,069 Average Effective Duration (yrs): 3.7
Total Management Fee ($)#: 9,561,990
Portfolio Turnover Rate (%): 26
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 96.4%
Money Market Funds 3.6%
Composition including fixed income credit
quality
AAA 2.7%
AA 34.4%
A 37.0%
BBB 13.6%
BB 3.5%
B 0.3%
Not Rated 4.9%
Money Market Funds 3.6%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000195152 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Municipal LimitedMaturity Fund
Class Name Class R6
Trading Symbol MTLRX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Municipal Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R6 $37 0.36%
Expenses Paid, Amount $ 37
Expense Ratio, Percent 0.36%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R6 shares of the MFS Municipal Limited Maturity Fund (fund) provided a total return of 5.19%, at net asset value. This compares with a return of 6.34% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg 1-9 Year Municipal Bond Index, generated a return of 4.91%.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • The municipal market produced positive returns over the trailing year, characterized by a supportive backdrop punctuated by bouts of volatility. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year, providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. Volatility rose again in March of this year due to heightened geopolitical risks and related economic effects before returning to relatively low levels late in the period. Resilient inflows and generally solid credit fundamentals were key supports for the asset class. The benchmark index for this fund generated a return of 4.91% for the period. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.03%, higher than the five-year average of 2.60%.
  • Top contributors to performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund’s overweight to the housing sector and underweight to general obligation bonds aided relative performance. Favorable security selection within both the transportation and education sectors also supported relative results.
    • From a quality perspective, an overweight to BBB-rated and below investment grade bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-9 Year Municipal Bond Index:
    • The fund's overweight to the 10 to 20-year segment of the yield curve detracted from relative returns as yields in that segment declined less than bonds with shorter maturities.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment*
This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
*For the period from the commencement of the class's investment operations, September 1, 2017 through April 30, 2026.
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr Life*
R6 without sales charge 5.19% 1.71% 2.21%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆ 6.34% 0.90% 2.20%
Bloomberg 1-9 Year Municipal Bond Index ∆ 4.91% 1.27% 1.85%
*
For the period from the commencement of the class's investment operations, September 1, 2017 through April 30, 2026.
∆
Source: FactSet Research Systems Inc.
Performance Inception Date Sep. 01, 2017
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r6 for more recent performance information.
Net Assets $ 3,116,903,553
Holdings Count | Holding 1,069
Advisory Fees Paid, Amount $ 9,561,990 [5]
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,116,903,553 Average Effective Maturity (yrs): 5.2
Total Number of Holdings: 1,069 Average Effective Duration (yrs): 3.7
Total Management Fee ($)#: 9,561,990
Portfolio Turnover Rate (%): 26
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 96.4%
Money Market Funds 3.6%
Composition including fixed income credit
quality
AAA 2.7%
AA 34.4%
A 37.0%
BBB 13.6%
BB 3.5%
B 0.3%
Not Rated 4.9%
Money Market Funds 3.6%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006760 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class A
Trading Symbol MRBFX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
A $61 0.60%
Expenses Paid, Amount $ 61
Expense Ratio, Percent 0.60%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class A shares of the MFS Total Return Bond Fund (fund) provided a total return of 4.40%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
A without sales charge 4.40% 0.49% 2.06%
A with initial sales charge (4.25%) (0.03)% (0.38)% 1.62%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/a for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [6]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006765 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class B
Trading Symbol MRBBX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
B $137 1.35%
Expenses Paid, Amount $ 137
Expense Ratio, Percent 1.35%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class B shares of the MFS Total Return Bond Fund (fund) provided a total return of 3.63%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
B without sales charge 3.63% (0.26)% 1.31%
B with CDSC (declining over six years from 4% to 0%)× (0.37)% (0.60)% 1.31%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
×
Assuming redemption at the end of the applicable period.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/b for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [7]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006766 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class C
Trading Symbol MRBCX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
C $148 1.45%
Expenses Paid, Amount $ 148
Expense Ratio, Percent 1.45%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class C shares of the MFS Total Return Bond Fund (fund) provided a total return of 3.52%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
C without sales charge 3.52% (0.36)% 1.20%
C with CDSC (1% for 12 months)× 2.52% (0.36)% 1.20%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
×
Assuming redemption at the end of the applicable period.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/c for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [8]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block] Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006767 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class I
Trading Symbol MRBIX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
I $46 0.45%
Expenses Paid, Amount $ 46
Expense Ratio, Percent 0.45%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class I shares of the MFS Total Return Bond Fund (fund) provided a total return of 4.56%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
I without sales charge 4.56% 0.64% 2.21%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/i for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [9]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006769 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class R1
Trading Symbol MRBGX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R1 $148 1.45%
Expenses Paid, Amount $ 148
Expense Ratio, Percent 1.45%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R1 shares of the MFS Total Return Bond Fund (fund) provided a total return of 3.52%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R1 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
R1 without sales charge 3.52% (0.34)% 1.20%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r1 for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [10]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006771 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class R2
Trading Symbol MRRRX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R2 $97 0.95%
Expenses Paid, Amount $ 97
Expense Ratio, Percent 0.95%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R2 shares of the MFS Total Return Bond Fund (fund) provided a total return of 4.04%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R2 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
R2 without sales charge 4.04% 0.14% 1.72%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r2 for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [11]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006772 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class R3
Trading Symbol MRBHX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R3 $72 0.70%
Expenses Paid, Amount $ 72
Expense Ratio, Percent 0.70%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R3 shares of the MFS Total Return Bond Fund (fund) provided a total return of 4.30%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R3 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
R3 without sales charge 4.30% 0.39% 1.96%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r3 for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [12]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006761 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class R4
Trading Symbol MRBJX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R4 $46 0.45%
Expenses Paid, Amount $ 46
Expense Ratio, Percent 0.45%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R4 shares of the MFS Total Return Bond Fund (fund) provided a total return of 4.56%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R4 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
R4 without sales charge 4.56% 0.64% 2.21%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r4 for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [13]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000034443 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Total Return Bond Fund
Class Name Class R6
Trading Symbol MRBKX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Total Return Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R6 $36 0.35%
Expenses Paid, Amount $ 36
Expense Ratio, Percent 0.35%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R6 shares of the MFS Total Return Bond Fund (fund) provided a total return of 4.66%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund's underweight exposure to the treasury sector and out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector aided relative returns. Favorable security selection within the industrials sector also supported relative results.
    • From a quality perspective, the fund’s out-of-benchmark exposure to BB-rated bonds benefited relative returns. Security selection within BBB-rated bonds was another positive factor for relative performance.
  • Top detractors from performance relative to the Bloomberg U.S. Aggregate Bond Index:
    • The fund’s underweight exposure to the mortgage backed securities (MBS) agency fixed rate sector weighed on relative performance. Not owning any securities within the government-related sovereign sector also held back relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.
Share Class 1-yr 5-yr 10-yr
R6 without sales charge 4.66% 0.74% 2.32%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r6 for more recent performance information.
Net Assets $ 8,274,986,056
Holdings Count | Holding 1,074
Advisory Fees Paid, Amount $ 28,761,662 [14]
Investment Company Portfolio Turnover 48.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,274,986,056 Average Effective Maturity (yrs): 7.4
Total Number of Holdings: 1,074 Average Effective Duration (yrs): 5.8
Total Management Fee ($)#: 28,761,662
Portfolio Turnover Rate (%): 48
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.5%
Money Market Funds 1.5%
Composition including fixed income credit quality
AAA 13.7%
AA 7.0%
A 10.8%
BBB 22.2%
BB 4.0%
B 1.9%
CCC 0.0%
CC 0.0%
U.S. Government 24.0%
Federal Agencies 14.7%
Not Rated 0.2%
Money Market Funds 1.5%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006716 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class B
Trading Symbol MFBBX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
B $154 1.51%
Expenses Paid, Amount $ 154
Expense Ratio, Percent 1.51%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class B shares of the MFS Corporate Bond Fund (fund) provided a total return of 4.42%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
B without sales charge 4.42% (0.30)% 1.83%
B with CDSC (declining over six years from 4% to 0%)× 0.42% (0.63)% 1.83%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
×
Assuming redemption at the end of the applicable period.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/b for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [15]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit
quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006711 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class A
Trading Symbol MFBFX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
A $78 0.76%
Expenses Paid, Amount $ 78
Expense Ratio, Percent 0.76%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class A shares of the MFS Corporate Bond Fund (fund) provided a total return of 5.20%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. This graph includes the deduction of the maximum applicable sales charge.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
A without sales charge 5.20% 0.44% 2.59%
A with initial sales charge (4.25%) 0.73% (0.42)% 2.14%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/a for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [16]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit
quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000119776 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class R6
Trading Symbol MQLKX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R6 $35 0.34%
Expenses Paid, Amount $ 35
Expense Ratio, Percent 0.34%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R6 shares of the MFS Limited Maturity Fund (fund) provided a total return of 4.28%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R6 without sales charge 4.28% 2.73% 2.64%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r6 for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [17]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006717 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class C
Trading Symbol MFBCX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
C $154 1.51%
Expenses Paid, Amount $ 154
Expense Ratio, Percent 1.51%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class C shares of the MFS Corporate Bond Fund (fund) provided a total return of 4.42%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
C without sales charge 4.42% (0.30)% 1.83%
C with CDSC (1% for 12 months)× 3.42% (0.30)% 1.83%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
×
Assuming redemption at the end of the applicable period.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/c for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [18]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit
quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006718 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class I
Trading Symbol MBDIX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
I $52 0.51%
Expenses Paid, Amount $ 52
Expense Ratio, Percent 0.51%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class I shares of the MFS Corporate Bond Fund (fund) provided a total return of 5.55%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
I without sales charge 5.55% 0.71% 2.84%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/i for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [19]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006720 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class R1
Trading Symbol MFBGX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R1 $154 1.51%
Expenses Paid, Amount $ 154
Expense Ratio, Percent 1.51%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R1 shares of the MFS Corporate Bond Fund (fund) provided a total return of 4.51%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R1 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R1 without sales charge 4.51% (0.28)% 1.84%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r1 for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [20]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006722 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class R2
Trading Symbol MBRRX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R2 $103 1.01%
Expenses Paid, Amount $ 103
Expense Ratio, Percent 1.01%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R2 shares of the MFS Corporate Bond Fund (fund) provided a total return of 4.94%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R2 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R2 without sales charge 4.94% 0.21% 2.34%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r2 for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [21]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006723 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class R3
Trading Symbol MFBHX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R3 $78 0.76%
Expenses Paid, Amount $ 78
Expense Ratio, Percent 0.76%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R3 shares of the MFS Corporate Bond Fund (fund) provided a total return of 5.20%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R3 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R3 without sales charge 5.20% 0.46% 2.60%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r3 for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [22]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006712 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class R4
Trading Symbol MFBJX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R4 $52 0.51%
Expenses Paid, Amount $ 52
Expense Ratio, Percent 0.51%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R4 shares of the MFS Corporate Bond Fund (fund) provided a total return of 5.63%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R4 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R4 without sales charge 5.63% 0.74% 2.87%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r4 for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [23]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000070424 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Fund
Class Name Class R6
Trading Symbol MFBKX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Corporate Bond Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R6 $42 0.41%
Expenses Paid, Amount $ 42
Expense Ratio, Percent 0.41%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R6 shares of the MFS Corporate Bond Fund (fund) provided a total return of 5.65%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg U.S. Credit Index, generated a return of 5.25%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg U.S. Credit Index:
    • The fund's out-of-benchmark exposure to both the BB and B-rated credit quality segments, and its overweight exposure to BBB-rated bonds, supported relative performance.
    • Favorable security selection within both A and BBB-rated bonds, particularly within the communications sector, also contributed to the fund's relative returns.
  • Top detractors from performance relative to the Bloomberg U.S. Credit Index:
    • The fund's underweight exposure to A-rated bonds held back relative performance.
    • Security selection within the energy sector also weakened relative returns.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R6 without sales charge 5.65% 0.80% 2.94%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg U.S. Credit Index ∆ 5.25% 0.65% 2.62%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r6 for more recent performance information.
Net Assets $ 4,394,650,297
Holdings Count | Holding 427
Advisory Fees Paid, Amount $ 16,745,757 [24]
Investment Company Portfolio Turnover 41.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 4,394,650,297 Average Effective Maturity (yrs): 9.3
Total Number of Holdings: 427 Average Effective Duration (yrs): 6.6
Total Management Fee ($)#: 16,745,757
Portfolio Turnover Rate (%): 41
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 3.2%
AA 2.7%
A 32.1%
BBB 50.0%
BB 7.0%
B 1.9%
D 0.2%
U.S. Government 1.1%
Not Rated 0.0%
Money Market Funds 1.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block] Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006745 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class A
Trading Symbol MQLFX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
A $58 0.57%
Expenses Paid, Amount $ 58
Expense Ratio, Percent 0.57%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class A shares of the MFS Limited Maturity Fund (fund) provided a total return of 4.04%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. This graph includes the deduction of the maximum applicable sales charge.
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
A without sales charge 4.04% 2.50% 2.41%
A with initial sales charge (2.50%) 1.44% 1.98% 2.16%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/a for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [25]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block] Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006750 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class B
Trading Symbol MQLBX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
B $134 1.32%
Expenses Paid, Amount $ 134
Expense Ratio, Percent 1.32%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class B shares of the MFS Limited Maturity Fund (fund) provided a total return of 3.44%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
B without sales charge 3.44% 1.77% 1.68%
B with CDSC (declining over six years from 4% to 0%)× (0.55)% 1.41% 1.68%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
×
Assuming redemption at the end of the applicable period.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/b for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [26]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block] Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006751 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class C
Trading Symbol MQLCX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
C $144 1.42%
Expenses Paid, Amount $ 144
Expense Ratio, Percent 1.42%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class C shares of the MFS Limited Maturity Fund (fund) provided a total return of 3.16%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
C without sales charge 3.16% 1.63% 1.57%
C with CDSC (1% for 12 months)× 2.17% 1.63% 1.57%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
×
Assuming redemption at the end of the applicable period.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/c for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [27]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block] Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006744 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class I
Trading Symbol MQLIX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
I $43 0.42%
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.42%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class I shares of the MFS Limited Maturity Fund (fund) provided a total return of 4.37%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
I without sales charge 4.37% 2.65% 2.58%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/i for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [28]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit
quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006753 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class R1
Trading Symbol MQLGX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R1 $144 1.42%
Expenses Paid, Amount $ 144
Expense Ratio, Percent 1.42%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R1 shares of the MFS Limited Maturity Fund (fund) provided a total return of 3.16%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R1 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R1 without sales charge 3.16% 1.60% 1.55%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r1 for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [29]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit
quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006755 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class R2
Trading Symbol MLMRX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R2 $84 0.82%
Expenses Paid, Amount $ 84
Expense Ratio, Percent 0.82%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R2 shares of the MFS Limited Maturity Fund (fund) provided a total return of 3.96%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R2 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R2 without sales charge 3.96% 2.24% 2.18%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r2 for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [30]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit
quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006756 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class R3
Trading Symbol MQLHX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R3 $68 0.67%
Expenses Paid, Amount $ 68
Expense Ratio, Percent 0.67%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R3 shares of the MFS Limited Maturity Fund (fund) provided a total return of 4.11%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R3 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R3 without sales charge 4.11% 2.40% 2.33%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r3 for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [31]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit
quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000006746 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Limited Maturity Fund
Class Name Class R4
Trading Symbol MQLJX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about MFS Limited Maturity Fund for the period of May 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website funds.mfs.com
Expenses [Text Block]
FUND EXPENSES
What were the fund costs for the last year?
(based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
R4 $43 0.42%
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.42%
Factors Affecting Performance [Text Block]
MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE
  • For the twelve months ended April 30, 2026, Class R4 shares of the MFS Limited Maturity Fund (fund) provided a total return of 4.20%, at net asset value. This compares with a return of 4.06% for the fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index. The fund's other benchmark, the Bloomberg 1-3 Year U.S. Government/Credit Bond Index, generated a return of 3.42%.
  • Global equity markets reached record levels during the period, withstanding considerable volatility amid tariffs, geopolitical conflict and high levels of uncertainty. A new geopolitical event distressed markets at the end of the period as US and Israeli forces launched strikes against Iran, disrupting Mideast oil and natural gas exports.  During the period, a pro-growth tax and spending bill was signed into law in the US, while in Europe, renewed focus on defense and infrastructure spending brightened the economic outlook. In Japan, the election of a pro-growth prime minister sent stocks to new highs prior to the conflict in Iran. Optimism over artificial intelligence remained high.
  • Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
  • Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
  • In fixed income markets, previously range-bound global bond yields spiked following the onset of the Middle East conflict, as energy-driven inflation fears appeared to have rattled bond investors. US rate volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) similarly rose from intra-period lows, reflecting uncertainty around the scope and duration of the conflict and its implications for global growth. However, volatility later retracted as the risk of a broader regional military escalation appeared less likely. Global credit spreads widened only modestly before stabilizing near prior levels, supported by strong demand and resilient underlying fundamentals.
  • Top contributors to performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • The fund's out-of-benchmark exposure to the collateralized mortgage obligation (CMO) sector strengthened relative performance. Security selection within the industrials sector also supported relative results.
    • From a quality perspective, security selection within BBB-rated bonds benefited relative returns.
  • Top detractors from performance relative to the Bloomberg 1-3 Year U.S. Government/Credit Bond Index:
    • There were no material detractors from relative performance during the reporting period.
Performance Past Does Not Indicate Future [Text] The fund’s past performance is not a good predictor of the fund’s future performance.
Line Graph [Table Text Block]
FUND PERFORMANCE
The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.
Growth of a Hypothetical $10,000 Investment
This graph shows the performance of a hypothetical $10,000 investment in Class R4 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns through 4/30/26
This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.
Share Class 1-yr 5-yr 10-yr
R4 without sales charge 4.20% 2.66% 2.61%
Comparative Benchmark(s)
Bloomberg U.S. Aggregate Bond Index ∆ 4.06% 0.18% 1.67%
Bloomberg 1-3 Year U.S. Government/Credit Bond Index ∆ 3.42% 2.07% 2.03%
∆
Source: FactSet Research Systems Inc.
No Deduction of Taxes [Text Block] The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.
Updated Performance Information Location [Text Block]
Visit mfs.com/perf/r4 for more recent performance information.
Net Assets $ 3,352,561,328
Holdings Count | Holding 396
Advisory Fees Paid, Amount $ 11,048,122 [32]
Investment Company Portfolio Turnover 50.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 3,352,561,328 Average Effective Maturity (yrs): 2.9
Total Number of Holdings: 396 Average Effective Duration (yrs): 2.1
Total Management Fee ($)#: 11,048,122
Portfolio Turnover Rate (%): 50
# Includes the effect of any management fee waivers, if applicable.
Where the fund holds derivatives, they are not included in the total number of portfolio holdings.
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 4/30/26)
Portfolio structure
Fixed Income 97.2%
Money Market Funds 2.8%
Composition including fixed income credit
quality
AAA 12.9%
AA 11.2%
A 18.6%
BBB 31.9%
CCC 0.0%
CC 0.0%
U.S. Government 22.2%
Federal Agencies 0.4%
Not Rated 0.0%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
[1] Includes the effect of any management fee waivers, if applicable.
[2] Includes the effect of any management fee waivers, if applicable.
[3] Includes the effect of any management fee waivers, if applicable.
[4] Includes the effect of any management fee waivers, if applicable.
[5] Includes the effect of any management fee waivers, if applicable.
[6] Includes the effect of any management fee waivers, if applicable.
[7] Includes the effect of any management fee waivers, if applicable.
[8] Includes the effect of any management fee waivers, if applicable.
[9] Includes the effect of any management fee waivers, if applicable.
[10] Includes the effect of any management fee waivers, if applicable.
[11] Includes the effect of any management fee waivers, if applicable.
[12] Includes the effect of any management fee waivers, if applicable.
[13] Includes the effect of any management fee waivers, if applicable.
[14] Includes the effect of any management fee waivers, if applicable.
[15] Includes the effect of any management fee waivers, if applicable.
[16] Includes the effect of any management fee waivers, if applicable.
[17] Includes the effect of any management fee waivers, if applicable.
[18] Includes the effect of any management fee waivers, if applicable.
[19] Includes the effect of any management fee waivers, if applicable.
[20] Includes the effect of any management fee waivers, if applicable.
[21] Includes the effect of any management fee waivers, if applicable.
[22] Includes the effect of any management fee waivers, if applicable.
[23] Includes the effect of any management fee waivers, if applicable.
[24] Includes the effect of any management fee waivers, if applicable.
[25] Includes the effect of any management fee waivers, if applicable.
[26] Includes the effect of any management fee waivers, if applicable.
[27] Includes the effect of any management fee waivers, if applicable.
[28] Includes the effect of any management fee waivers, if applicable.
[29] Includes the effect of any management fee waivers, if applicable.
[30] Includes the effect of any management fee waivers, if applicable.
[31] Includes the effect of any management fee waivers, if applicable.
[32] Includes the effect of any management fee waivers, if applicable.