v3.26.3
Shareholder Report
 6 Months Ended
Aug. 31, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name MFS SERIES TRUST XIII
Entity Central Index Key 0000356349
Entity Investment Company Type N-1A
Document Period End Date Aug. 31, 2026
C000117927 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class R6
Trading Symbol MFGKX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R6 $21 0.42%
Expenses Paid, Amount $ 21
Expense Ratio, Percent 0.42%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000002008 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class R4
Trading Symbol MFGJX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R4 $26 0.52%
Expenses Paid, Amount $ 26
Expense Ratio, Percent 0.52%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000002018 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class R3
Trading Symbol MFGHX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R3 $38 0.77%
Expenses Paid, Amount $ 38
Expense Ratio, Percent 0.77%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000002017 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class R2
Trading Symbol MGVSX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R2 $51 1.02%
Expenses Paid, Amount $ 51
Expense Ratio, Percent 1.02%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000002015 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class R1
Trading Symbol MFGGX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R1 $76 1.52%
Expenses Paid, Amount $ 76
Expense Ratio, Percent 1.52%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000002006 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class I
Trading Symbol MGSIX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
I $26 0.52%
Expenses Paid, Amount $ 26
Expense Ratio, Percent 0.52%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000002013 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class C
Trading Symbol MFGDX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
C $75 1.52%
Expenses Paid, Amount $ 75
Expense Ratio, Percent 1.52%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000002012 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class B
Trading Symbol MFGBX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
B $75 1.52%
Expenses Paid, Amount $ 75
Expense Ratio, Percent 1.52%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000002007 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Fund
Class Name Class A
Trading Symbol MFGSX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
A $38 0.77%
Expenses Paid, Amount $ 38
Expense Ratio, Percent 0.77%
Net Assets $ 1,916,146,033
Holdings Count | Holding 812
Investment Company Portfolio Turnover 87.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,916,146,033 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 812 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 87
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 8/31/26)
Portfolio structure
Fixed Income 91.8%
Money Market Funds 8.2%
Composition including fixed income credit
quality
AAA 6.3%
AA 1.4%
A 0.2%
U.S. Government 27.1%
Federal Agencies 56.8%
Money Market Funds 8.2%
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.
C000033358 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® DiversifiedIncome Fund
Class Name Class A
Trading Symbol DIFAX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Diversified Income Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized) ~
A $45 0.89%
˜ Expenses are direct expenses and do not include underlying fund fees and expenses.
Expenses Paid, Amount $ 45 [1]
Expense Ratio, Percent 0.89% [1]
Net Assets $ 1,771,014,850
Holdings Count | Holding 1,376
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,771,014,850 Portfolio Turnover Rate (%): 22
Total Number of Holdings: 1,376
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 8/31/26)
Portfolio structure
Fixed Income ~ 61.4%
Equities 37.0%
Money Market Funds 1.5%
Purchased Options 0.1%
Equity sectors
Real Estate 12.5%
Health Care 4.9%
Financials 4.2%
Consumer Staples 3.6%
Energy 2.9%
Industrials 2.4%
Consumer Discretionary 1.9%
Information Technology 1.6%
Utilities 1.4%
Communication Services 1.0%
Materials 0.5%
Convertible Debt 0.1%
Composition including fixed income credit quality
AAA 1.2%
AA 0.9%
A 6.2%
BBB 12.2%
BB 16.2%
B 10.9%
CCC 3.0%
CC 0.0%
C 0.2%
D 0.2%
U.S. Government 3.8%
Federal Agencies 5.9%
Not Rated 0.7%
Non-Fixed Income 37.1%
Money Market Funds 1.5%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
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.
~ The fund invests a portion of its assets in Exchange-Traded Funds (ETFs) or Options on ETFs to gain fixed income exposure. Percentages include the direct exposure from investing in ETFs or Options on ETFs and not the indirect exposure to the underlying holdings.
The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.
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.
C000033359 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® DiversifiedIncome Fund
Class Name Class C
Trading Symbol DIFCX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Diversified Income Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized) ~
C $83 1.64%
˜ Expenses are direct expenses and do not include underlying fund fees and expenses.
Expenses Paid, Amount $ 83 [2]
Expense Ratio, Percent 1.64% [2]
Net Assets $ 1,771,014,850
Holdings Count | Holding 1,376
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,771,014,850 Portfolio Turnover Rate (%): 22
Total Number of Holdings: 1,376
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 8/31/26)
Portfolio structure
Fixed Income ~ 61.4%
Equities 37.0%
Money Market Funds 1.5%
Purchased Options 0.1%
Equity sectors
Real Estate 12.5%
Health Care 4.9%
Financials 4.2%
Consumer Staples 3.6%
Energy 2.9%
Industrials 2.4%
Consumer Discretionary 1.9%
Information Technology 1.6%
Utilities 1.4%
Communication Services 1.0%
Materials 0.5%
Convertible Debt 0.1%
Composition including fixed income credit quality
AAA 1.2%
AA 0.9%
A 6.2%
BBB 12.2%
BB 16.2%
B 10.9%
CCC 3.0%
CC 0.0%
C 0.2%
D 0.2%
U.S. Government 3.8%
Federal Agencies 5.9%
Not Rated 0.7%
Non-Fixed Income 37.1%
Money Market Funds 1.5%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
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.
~ The fund invests a portion of its assets in Exchange-Traded Funds (ETFs) or Options on ETFs to gain fixed income exposure. Percentages include the direct exposure from investing in ETFs or Options on ETFs and not the indirect exposure to the underlying holdings.
The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.
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.
C000033360 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® DiversifiedIncome Fund
Class Name Class I
Trading Symbol DIFIX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Diversified Income Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized) ~
I $33 0.64%
˜ Expenses are direct expenses and do not include underlying fund fees and expenses.
Expenses Paid, Amount $ 33 [3]
Expense Ratio, Percent 0.64% [3]
Net Assets $ 1,771,014,850
Holdings Count | Holding 1,376
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,771,014,850 Portfolio Turnover Rate (%): 22
Total Number of Holdings: 1,376
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 8/31/26)
Portfolio structure
Fixed Income ~ 61.4%
Equities 37.0%
Money Market Funds 1.5%
Purchased Options 0.1%
Equity sectors
Real Estate 12.5%
Health Care 4.9%
Financials 4.2%
Consumer Staples 3.6%
Energy 2.9%
Industrials 2.4%
Consumer Discretionary 1.9%
Information Technology 1.6%
Utilities 1.4%
Communication Services 1.0%
Materials 0.5%
Convertible Debt 0.1%
Composition including fixed income credit quality
AAA 1.2%
AA 0.9%
A 6.2%
BBB 12.2%
BB 16.2%
B 10.9%
CCC 3.0%
CC 0.0%
C 0.2%
D 0.2%
U.S. Government 3.8%
Federal Agencies 5.9%
Not Rated 0.7%
Non-Fixed Income 37.1%
Money Market Funds 1.5%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
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.
~ The fund invests a portion of its assets in Exchange-Traded Funds (ETFs) or Options on ETFs to gain fixed income exposure. Percentages include the direct exposure from investing in ETFs or Options on ETFs and not the indirect exposure to the underlying holdings.
The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.
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.
C000068409 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® DiversifiedIncome Fund
Class Name Class R1
Trading Symbol DIFDX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Diversified Income Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized) ~
R1 $83 1.64%
˜ Expenses are direct expenses and do not include underlying fund fees and expenses.
Expenses Paid, Amount $ 83 [4]
Expense Ratio, Percent 1.64% [4]
Net Assets $ 1,771,014,850
Holdings Count | Holding 1,376
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,771,014,850 Portfolio Turnover Rate (%): 22
Total Number of Holdings: 1,376
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 8/31/26)
Portfolio structure
Fixed Income ~ 61.4%
Equities 37.0%
Money Market Funds 1.5%
Purchased Options 0.1%
Equity sectors
Real Estate 12.5%
Health Care 4.9%
Financials 4.2%
Consumer Staples 3.6%
Energy 2.9%
Industrials 2.4%
Consumer Discretionary 1.9%
Information Technology 1.6%
Utilities 1.4%
Communication Services 1.0%
Materials 0.5%
Convertible Debt 0.1%
Composition including fixed income credit quality
AAA 1.2%
AA 0.9%
A 6.2%
BBB 12.2%
BB 16.2%
B 10.9%
CCC 3.0%
CC 0.0%
C 0.2%
D 0.2%
U.S. Government 3.8%
Federal Agencies 5.9%
Not Rated 0.7%
Non-Fixed Income 37.1%
Money Market Funds 1.5%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
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.
~ The fund invests a portion of its assets in Exchange-Traded Funds (ETFs) or Options on ETFs to gain fixed income exposure. Percentages include the direct exposure from investing in ETFs or Options on ETFs and not the indirect exposure to the underlying holdings.
The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.
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.
C000068410 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® DiversifiedIncome Fund
Class Name Class R2
Trading Symbol DIFEX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Diversified Income Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized) ~
R2 $58 1.14%
˜ Expenses are direct expenses and do not include underlying fund fees and expenses.
Expenses Paid, Amount $ 58 [5]
Expense Ratio, Percent 1.14% [5]
Net Assets $ 1,771,014,850
Holdings Count | Holding 1,376
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,771,014,850 Portfolio Turnover Rate (%): 22
Total Number of Holdings: 1,376
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 8/31/26)
Portfolio structure
Fixed Income ~ 61.4%
Equities 37.0%
Money Market Funds 1.5%
Purchased Options 0.1%
Equity sectors
Real Estate 12.5%
Health Care 4.9%
Financials 4.2%
Consumer Staples 3.6%
Energy 2.9%
Industrials 2.4%
Consumer Discretionary 1.9%
Information Technology 1.6%
Utilities 1.4%
Communication Services 1.0%
Materials 0.5%
Convertible Debt 0.1%
Composition including fixed income credit quality
AAA 1.2%
AA 0.9%
A 6.2%
BBB 12.2%
BB 16.2%
B 10.9%
CCC 3.0%
CC 0.0%
C 0.2%
D 0.2%
U.S. Government 3.8%
Federal Agencies 5.9%
Not Rated 0.7%
Non-Fixed Income 37.1%
Money Market Funds 1.5%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
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.
~ The fund invests a portion of its assets in Exchange-Traded Funds (ETFs) or Options on ETFs to gain fixed income exposure. Percentages include the direct exposure from investing in ETFs or Options on ETFs and not the indirect exposure to the underlying holdings.
The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.
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.
C000068411 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® DiversifiedIncome Fund
Class Name Class R3
Trading Symbol DIFFX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Diversified Income Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized) ~
R3 $45 0.89%
˜ Expenses are direct expenses and do not include underlying fund fees and expenses.
Expenses Paid, Amount $ 45 [6]
Expense Ratio, Percent 0.89% [6]
Net Assets $ 1,771,014,850
Holdings Count | Holding 1,376
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,771,014,850 Portfolio Turnover Rate (%): 22
Total Number of Holdings: 1,376
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 8/31/26)
Portfolio structure
Fixed Income ~ 61.4%
Equities 37.0%
Money Market Funds 1.5%
Purchased Options 0.1%
Equity sectors
Real Estate 12.5%
Health Care 4.9%
Financials 4.2%
Consumer Staples 3.6%
Energy 2.9%
Industrials 2.4%
Consumer Discretionary 1.9%
Information Technology 1.6%
Utilities 1.4%
Communication Services 1.0%
Materials 0.5%
Convertible Debt 0.1%
Composition including fixed income credit quality
AAA 1.2%
AA 0.9%
A 6.2%
BBB 12.2%
BB 16.2%
B 10.9%
CCC 3.0%
CC 0.0%
C 0.2%
D 0.2%
U.S. Government 3.8%
Federal Agencies 5.9%
Not Rated 0.7%
Non-Fixed Income 37.1%
Money Market Funds 1.5%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
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.
~ The fund invests a portion of its assets in Exchange-Traded Funds (ETFs) or Options on ETFs to gain fixed income exposure. Percentages include the direct exposure from investing in ETFs or Options on ETFs and not the indirect exposure to the underlying holdings.
The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.
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.
C000068412 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® DiversifiedIncome Fund
Class Name Class R4
Trading Symbol DIFGX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Diversified Income Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized) ~
R4 $33 0.64%
˜ Expenses are direct expenses and do not include underlying fund fees and expenses.
Expenses Paid, Amount $ 33 [7]
Expense Ratio, Percent 0.64% [7]
Net Assets $ 1,771,014,850
Holdings Count | Holding 1,376
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,771,014,850 Portfolio Turnover Rate (%): 22
Total Number of Holdings: 1,376
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 8/31/26)
Portfolio structure
Fixed Income ~ 61.4%
Equities 37.0%
Money Market Funds 1.5%
Purchased Options 0.1%
Equity sectors
Real Estate 12.5%
Health Care 4.9%
Financials 4.2%
Consumer Staples 3.6%
Energy 2.9%
Industrials 2.4%
Consumer Discretionary 1.9%
Information Technology 1.6%
Utilities 1.4%
Communication Services 1.0%
Materials 0.5%
Convertible Debt 0.1%
Composition including fixed income credit
quality
AAA 1.2%
AA 0.9%
A 6.2%
BBB 12.2%
BB 16.2%
B 10.9%
CCC 3.0%
CC 0.0%
C 0.2%
D 0.2%
U.S. Government 3.8%
Federal Agencies 5.9%
Not Rated 0.7%
Non-Fixed Income 37.1%
Money Market Funds 1.5%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
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.
~ The fund invests a portion of its assets in Exchange-Traded Funds (ETFs) or Options on ETFs to gain fixed income exposure. Percentages include the direct exposure from investing in ETFs or Options on ETFs and not the indirect exposure to the underlying holdings.
The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.
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.
C000117928 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® DiversifiedIncome Fund
Class Name Class R6
Trading Symbol DIFHX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Diversified Income Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized) ~
R6 $28 0.55%
˜ Expenses are direct expenses and do not include underlying fund fees and expenses.
Expenses Paid, Amount $ 28 [8]
Expense Ratio, Percent 0.55% [8]
Net Assets $ 1,771,014,850
Holdings Count | Holding 1,376
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 1,771,014,850 Portfolio Turnover Rate (%): 22
Total Number of Holdings: 1,376
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 8/31/26)
Portfolio structure
Fixed Income ~ 61.4%
Equities 37.0%
Money Market Funds 1.5%
Purchased Options 0.1%
Equity sectors
Real Estate 12.5%
Health Care 4.9%
Financials 4.2%
Consumer Staples 3.6%
Energy 2.9%
Industrials 2.4%
Consumer Discretionary 1.9%
Information Technology 1.6%
Utilities 1.4%
Communication Services 1.0%
Materials 0.5%
Convertible Debt 0.1%
Composition including fixed income credit
quality
AAA 1.2%
AA 0.9%
A 6.2%
BBB 12.2%
BB 16.2%
B 10.9%
CCC 3.0%
CC 0.0%
C 0.2%
D 0.2%
U.S. Government 3.8%
Federal Agencies 5.9%
Not Rated 0.7%
Non-Fixed Income 37.1%
Money Market Funds 1.5%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
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.
~ The fund invests a portion of its assets in Exchange-Traded Funds (ETFs) or Options on ETFs to gain fixed income exposure. Percentages include the direct exposure from investing in ETFs or Options on ETFs and not the indirect exposure to the underlying holdings.
The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.
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.
C000117930 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class R6
Trading Symbol NDVVX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R6 $45 0.87%
Expenses Paid, Amount $ 45
Expense Ratio, Percent 0.87%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
C000100963 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class R4
Trading Symbol NDVUX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R4 $51 0.98%
Expenses Paid, Amount $ 51
Expense Ratio, Percent 0.98%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
C000100962 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class R3
Trading Symbol NDVTX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R3 $63 1.22%
Expenses Paid, Amount $ 63
Expense Ratio, Percent 1.22%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
C000100961 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class R2
Trading Symbol NDVSX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R2 $77 1.48%
Expenses Paid, Amount $ 77
Expense Ratio, Percent 1.48%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
C000100960 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class R1
Trading Symbol NDVRX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R1 $102 1.98%
Expenses Paid, Amount $ 102
Expense Ratio, Percent 1.98%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
C000100959 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class I
Trading Symbol NDVIX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
I $51 0.98%
Expenses Paid, Amount $ 51
Expense Ratio, Percent 0.98%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
C000100958 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class C
Trading Symbol NDVCX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
C $103 1.98%
Expenses Paid, Amount $ 103
Expense Ratio, Percent 1.98%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
C000100957 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class B
Trading Symbol NDVBX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
B $102 1.97%
Expenses Paid, Amount $ 102
Expense Ratio, Percent 1.97%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
C000100956 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® New DiscoveryValue Fund
Class Name Class A
Trading Symbol NDVAX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS New Discovery Value Fund for the period of March 1, 2026 to August 31, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
A $64 1.23%
Expenses Paid, Amount $ 64
Expense Ratio, Percent 1.23%
Net Assets $ 2,285,841,364
Holdings Count | Holding 146
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 8/31/26
Net Assets ($): 2,285,841,364 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 146
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 8/31/26)
Portfolio structure
Equities 97.6%
Money Market Funds 2.4%
Equity sectors
Financials 25.0%
Health Care 12.6%
Industrials 11.6%
Consumer Discretionary 9.1%
Information Technology 8.8%
Energy 7.9%
Real Estate 7.8%
Utilities 6.0%
Materials 5.7%
Consumer Staples 2.0%
Communication Services 1.1%
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
Plains GP Holdings LP 1.4%
Cathay General Bancorp, Inc. 1.3%
United Community Bank, Inc. 1.2%
Prosperity Bancshares, Inc. 1.2%
Hancock Whitney Corp. 1.2%
First Interstate BancSystem, Inc. 1.2%
Columbia Banking System, Inc. 1.2%
CVB Financial Corp. 1.1%
M/I Homes, Inc. 1.1%
Popular, Inc. 1.1%
[1] Expenses are direct expenses and do not include underlying fund fees and expenses.
[2] Expenses are direct expenses and do not include underlying fund fees and expenses.
[3] Expenses are direct expenses and do not include underlying fund fees and expenses.
[4] Expenses are direct expenses and do not include underlying fund fees and expenses.
[5] Expenses are direct expenses and do not include underlying fund fees and expenses.
[6] Expenses are direct expenses and do not include underlying fund fees and expenses.
[7] Expenses are direct expenses and do not include underlying fund fees and expenses.
[8] Expenses are direct expenses and do not include underlying fund fees and expenses.