v3.26.1
Fees and Expenses
Apr. 30, 2026
USD ($)
MFS Corporate Bond Fund  
Prospectus [Line Items]  
Expense Heading [Optional Text] Fees and Expenses
Expense Narrative [Text Block]

This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below.

You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $100,000 in MFS funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers and Reductions” on page 11 and “Appendix A – Waivers and Reductions of Sales Charges” on page A-1 of the fund’s prospectus.

Expense Breakpoint Discounts [Text] You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $100,000 in MFS funds.
Expense Breakpoint, Minimum Investment Required [Amount] $ 100,000
Shareholder Fees Caption [Optional Text] Shareholder Fees (fees paid directly from your investment):
Shareholder Fees [Table]
Shareholder Fees - MFS Corporate Bond Fund
Class A
Class B
Class C
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) 4.25% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) 1.00% [1] 4.00% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
[1] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
Operating Expenses Caption [Optional Text] Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Annual Fund Operating Expenses [Table]
Annual Fund Operating Expenses - MFS Corporate Bond Fund
Class A
Class B
Class C
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Management Fees (as a percentage of Assets) 0.38% 0.38% 0.38% 0.38% 0.38% 0.38% 0.38% 0.38% 0.38%
Distribution and Service (12b-1) Fees 0.25% 1.00% 1.00% 0.00% 1.00% 0.50% 0.25% 0.00% 0.00%
Other Expenses (as a percentage of Assets): 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.04%
Expenses (as a percentage of Assets) 0.76% 1.51% 1.51% 0.51% 1.51% 1.01% 0.76% 0.51% 0.42%
Fee Waiver or Reimbursement [1] (0.01%) (0.01%) (0.01%) (0.01%) (0.01%) (0.01%) (0.01%) (0.01%) (0.01%)
Net Expenses (as a percentage of Assets) 0.75% 1.50% 1.50% 0.50% 1.50% 1.00% 0.75% 0.50% 0.41%
Fee Waiver or Reimbursement over Assets, Date of Termination August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027
[1] Massachusetts Financial Services Company (MFS) has agreed in writing to waive at least 0.01% of the fund's management fee as part of an agreement pursuant to which MFS has agreed to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027.
Expense Example [Heading] Example
Expense Example Narrative [Text Block]

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.

The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Expense Example by, Year, Caption [Text] Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Expense Example, With Redemption [Table]
Expense Example - MFS Corporate Bond Fund - USD ($)
Class A
Class B
 [1]
Class C
 [1]
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Expense Example, with Redemption, 1 Year $ 498 $ 553 $ 253 $ 51 $ 153 $ 102 $ 77 $ 51 $ 42
Expense Example, with Redemption, 3 Years 657 776 476 163 476 321 242 163 134
Expense Example, with Redemption, 5 Years 828 1,023 823 284 823 557 421 284 234
Expense Example, with Redemption, 10 Years $ 1,326 $ 1,598 $ 1,598 $ 640 $ 1,801 $ 1,235 $ 941 $ 640 $ 529
[1] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.
Expense Example, No Redemption [Table]
Expense Example, No Redemption - MFS Corporate Bond Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 153 $ 153
Expense Example, No Redemption, 3 Years [1] 476 476
Expense Example, No Redemption, 5 Years [1] 823 823
Expense Example, No Redemption, 10 Years [1] $ 1,598 $ 1,598
[1] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.
Portfolio Turnover [Heading] Portfolio Turnover
Portfolio Turnover [Text Block]

The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 41% of the average value of its portfolio.
Portfolio Turnover, Rate 41.00%
MFS Corporate Bond Fund | Class A  
Prospectus [Line Items]  
Expenses Deferred Charges [Text Block] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
MFS Limited Maturity Fund  
Prospectus [Line Items]  
Expense Heading [Optional Text] Fees and Expenses
Expense Narrative [Text Block]

This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below.

You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers and Reductions” on page 11 and “Appendix A – Waivers and Reductions of Sales Charges” on page A-1 of the fund’s prospectus.

Expense Breakpoint Discounts [Text] You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS funds.
Expense Breakpoint, Minimum Investment Required [Amount] $ 50,000
Shareholder Fees Caption [Optional Text] Shareholder Fees (fees paid directly from your investment):
Shareholder Fees [Table]
Shareholder Fees - MFS Limited Maturity Fund
Class A
Class B
Class C
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) 2.50% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) 0.75% [1] 4.00% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
[1] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
Operating Expenses Caption [Optional Text] Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Annual Fund Operating Expenses [Table]
Annual Fund Operating Expenses - MFS Limited Maturity Fund
Class A
Class B
Class C
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Management Fees (as a percentage of Assets) 0.35% 0.35% 0.35% 0.35% 0.35% 0.35% 0.35% 0.35% 0.35%
Distribution and Service (12b-1) Fees 0.25% 1.00% 1.00% 0.00% 1.00% 0.50% 0.25% 0.00% 0.00%
Other Expenses (as a percentage of Assets): 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.05%
Expenses (as a percentage of Assets) 0.73% 1.48% 1.48% 0.48% 1.48% 0.98% 0.73% 0.48% 0.40%
Fee Waiver or Reimbursement [1] (0.16%) (0.16%) (0.06%) (0.06%) (0.06%) (0.16%) (0.06%) (0.06%) (0.06%)
Net Expenses (as a percentage of Assets) 0.57% 1.32% 1.42% 0.42% 1.42% 0.82% 0.67% 0.42% 0.34%
Fee Waiver or Reimbursement over Assets, Date of Termination August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027
[1] Massachusetts Financial Services Company (MFS) has agreed in writing to waive at least 0.01% of the fund's management fee as part of an agreement pursuant to which MFS has agreed to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027. MFS Fund Distributors, Inc. (MFD), has agreed in writing to waive the Class A and Class B service fee to 0.15% of each class' average daily net assets annually until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027. MFD has agreed in writing to waive the Class R2 distribution fee to 0.15% of the class' average daily net assets annually until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027. MFS has agreed in writing to bear the fund's expenses, excluding management fees, distribution and service fees, payments made to service providers (other than MFS Service Center, Inc.) that provide certain sub-accounting services, interest, taxes, extraordinary expenses, brokerage and transaction costs, certain tax reclaim recovery expenses (including contingency fees and closing agreement expenses), and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each class of shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027.
Expense Example [Heading] Example
Expense Example Narrative [Text Block]

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.

The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Expense Example by, Year, Caption [Text] Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Expense Example, With Redemption [Table]
Expense Example - MFS Limited Maturity Fund - USD ($)
Class A
Class B
 [1]
Class C
 [1]
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Expense Example, with Redemption, 1 Year $ 307 $ 534 $ 245 $ 43 $ 145 $ 84 $ 68 $ 43 $ 35
Expense Example, with Redemption, 3 Years 462 752 462 148 462 296 227 148 122
Expense Example, with Redemption, 5 Years 630 993 802 263 802 526 400 263 218
Expense Example, with Redemption, 10 Years $ 1,119 $ 1,551 $ 1,560 $ 598 $ 1,763 $ 1,187 $ 901 $ 598 $ 499
[1] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.
Expense Example, No Redemption [Table]
Expense Example, No Redemption - MFS Limited Maturity Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 134 $ 145
Expense Example, No Redemption, 3 Years [1] 452 462
Expense Example, No Redemption, 5 Years [1] 793 802
Expense Example, No Redemption, 10 Years [1] $ 1,551 $ 1,560
[1] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.
Portfolio Turnover [Heading] Portfolio Turnover
Portfolio Turnover [Text Block]

The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 50% of the average value of its portfolio.
Portfolio Turnover, Rate 50.00%
MFS Limited Maturity Fund | Class A  
Prospectus [Line Items]  
Expenses Deferred Charges [Text Block] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
MFS Municipal Limited Maturity Fund  
Prospectus [Line Items]  
Expense Heading [Optional Text] Fees and Expenses
Expense Narrative [Text Block]

This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below.

You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers and Reductions” on page 11 and “Appendix A – Waivers and Reductions of Sales Charges” on page A-1 of the fund’s prospectus.

Expense Breakpoint Discounts [Text] You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS funds.
Expense Breakpoint, Minimum Investment Required [Amount] $ 50,000
Shareholder Fees Caption [Optional Text] Shareholder Fees (fees paid directly from your investment):
Shareholder Fees [Table]
Shareholder Fees - MFS Municipal Limited Maturity Fund
Class A
Class B
Class C
Class I
Class R6
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) 2.50% 0.00% 0.00% 0.00% 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) 0.75% [1] 4.00% 1.00% 0.00% 0.00%
[1] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
Operating Expenses Caption [Optional Text] Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Annual Fund Operating Expenses [Table]
Annual Fund Operating Expenses - MFS Municipal Limited Maturity Fund
Class A
Class B
Class C
Class I
Class R6
Management Fees (as a percentage of Assets) 0.34% 0.34% 0.34% 0.34% 0.34%
Distribution and Service (12b-1) Fees 0.25% 1.00% 1.00% 0.00% 0.00%
Other Expenses (as a percentage of Assets): 0.12% 0.12% 0.12% 0.12% 0.05%
Expenses (as a percentage of Assets) 0.71% 1.46% 1.46% 0.46% 0.39%
Fee Waiver or Reimbursement [1] (0.12%) (0.12%) (0.02%) (0.02%) (0.03%)
Net Expenses (as a percentage of Assets) 0.59% 1.34% 1.44% 0.44% 0.36%
Fee Waiver or Reimbursement over Assets, Date of Termination August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027
[1] Massachusetts Financial Services Company (MFS) has agreed in writing to waive at least 0.01% of the fund's management fee as part of an agreement pursuant to which MFS has agreed to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027. MFS Fund Distributors, Inc. (MFD), has agreed in writing to waive the Class A and Class B service fee to 0.15% of each class' average daily net assets annually until modified by the fund’s Board of Trustees, but such agreement will continue until at least August 31, 2027. MFS has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, certain tax reclaim recovery expenses (including contingency fees and closing agreement expenses), and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Total Annual Fund Operating Expenses" do not exceed 0.59% of the class' average daily net assets annually for Class A shares, 1.34% of the class' average daily net assets annually for Class B shares, 1.44% of the class' average daily net assets annually for Class C shares, 0.44% of the class' average daily net assets annually for Class I shares, and 0.36% of the class' average daily net assets annually for Class R6 shares. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue until at least August 31, 2027.
Expense Example [Heading] Example
Expense Example Narrative [Text Block]

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.

The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Expense Example by, Year, Caption [Text] Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Expense Example, With Redemption [Table]
Expense Example - MFS Municipal Limited Maturity Fund - USD ($)
Class A
Class B
 [1]
Class C
 [1]
Class I
Class R6
Expense Example, with Redemption, 1 Year $ 309 $ 536 $ 247 $ 45 $ 37
Expense Example, with Redemption, 3 Years 460 750 460 146 122
Expense Example, with Redemption, 5 Years 624 986 796 256 216
Expense Example, with Redemption, 10 Years $ 1,099 $ 1,532 $ 1,541 $ 577 $ 490
[1] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.
Expense Example, No Redemption [Table]
Expense Example, No Redemption - MFS Municipal Limited Maturity Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 136 $ 147
Expense Example, No Redemption, 3 Years [1] 450 460
Expense Example, No Redemption, 5 Years [1] 786 796
Expense Example, No Redemption, 10 Years [1] $ 1,532 $ 1,541
[1] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.
Portfolio Turnover [Heading] Portfolio Turnover
Portfolio Turnover [Text Block]

The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 26% of the average value of its portfolio.
Portfolio Turnover, Rate 26.00%
MFS Municipal Limited Maturity Fund | Class A  
Prospectus [Line Items]  
Expenses Deferred Charges [Text Block] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
MFS Total Return Bond Fund  
Prospectus [Line Items]  
Expense Heading [Optional Text] Fees and Expenses
Expense Narrative [Text Block]

This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below.

You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $100,000 in MFS funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers and Reductions” on page 13 and “Appendix A – Waivers and Reductions of Sales Charges” on page A-1 of the fund’s prospectus.

Expense Breakpoint Discounts [Text] You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $100,000 in MFS funds.
Expense Breakpoint, Minimum Investment Required [Amount] $ 100,000
Shareholder Fees Caption [Optional Text] Shareholder Fees (fees paid directly from your investment):
Shareholder Fees [Table]
Shareholder Fees - MFS Total Return Bond Fund
Class A
Class B
Class C
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) 4.25% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) 1.00% [1] 4.00% 1.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
[1] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
Operating Expenses Caption [Optional Text] Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Annual Fund Operating Expenses [Table]
Annual Fund Operating Expenses - MFS Total Return Bond Fund
Class A
Class B
Class C
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Management Fees (as a percentage of Assets) 0.39% 0.39% 0.39% 0.39% 0.39% 0.39% 0.39% 0.39% 0.39%
Distribution and Service (12b-1) Fees 0.25% 1.00% 1.00% 0.00% 1.00% 0.50% 0.25% 0.00% 0.00%
Other Expenses (as a percentage of Assets): 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.13% 0.03%
Expenses (as a percentage of Assets) 0.77% 1.52% 1.52% 0.52% 1.52% 1.02% 0.77% 0.52% 0.42%
Fee Waiver or Reimbursement [1] (0.17%) (0.17%) (0.07%) (0.07%) (0.07%) (0.07%) (0.07%) (0.07%) (0.06%)
Net Expenses (as a percentage of Assets) 0.60% 1.35% 1.45% 0.45% 1.45% 0.95% 0.70% 0.45% 0.36%
Fee Waiver or Reimbursement over Assets, Date of Termination August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027 August 31, 2027
[1] Massachusetts Financial Services Company (MFS) has agreed in writing to reduce its management fee to 0.40% of the fund’s average daily net assets annually up to $2.5 billion. This written agreement will remain in effect until modified by the fund’s Board of Trustees, but such agreement will continue until at least August 31, 2027. MFS has agreed in writing to waive at least 0.01% of the fund's management fee as part of an agreement pursuant to which MFS has agreed to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027. MFS Fund Distributors, Inc. (MFD), has agreed in writing to waive the Class A and Class B service fee to 0.15% of each class' average daily net assets annually until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027. MFS has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, certain tax reclaim recovery expenses (including contingency fees and closing agreement expenses), and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Total Annual Fund Operating Expenses" do not exceed 0.60% of the class' average daily net assets annually for Class A shares, 1.35% of the class' average daily net assets annually for Class B shares, 1.45% of the class' average daily net assets annually for each of Class C and Class R1 shares, 0.45% of the class' average daily net assets annually for each of Class I and Class R4 shares, 0.95% of the class' average daily net assets annually for Class R2 shares, 0.70% of the class' average daily net assets annually for Class R3 shares, and 0.36% of the class' average daily net assets annually for Class R6 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027.
Expense Example [Heading] Example
Expense Example Narrative [Text Block]

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.

The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Expense Example by, Year, Caption [Text] Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Expense Example, With Redemption [Table]
Expense Example - MFS Total Return Bond Fund - USD ($)
Class A
Class B
 [1]
Class C
 [1]
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Expense Example, with Redemption, 1 Year $ 484 $ 537 $ 248 $ 46 $ 148 $ 97 $ 72 $ 46 $ 37
Expense Example, with Redemption, 3 Years 644 764 473 160 473 318 239 160 129
Expense Example, with Redemption, 5 Years 819 1,013 822 284 822 556 421 284 229
Expense Example, with Redemption, 10 Years $ 1,323 $ 1,595 $ 1,604 $ 646 $ 1,807 $ 1,242 $ 948 $ 646 $ 524
[1] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.
Expense Example, No Redemption [Table]
Expense Example, No Redemption - MFS Total Return Bond Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 137 $ 148
Expense Example, No Redemption, 3 Years [1] 464 473
Expense Example, No Redemption, 5 Years [1] 813 822
Expense Example, No Redemption, 10 Years [1] $ 1,595 $ 1,604
[1] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.
Portfolio Turnover [Heading] Portfolio Turnover
Portfolio Turnover [Text Block]

The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 48% of the average value of its portfolio (22% excluding to be announced (TBA) transactions).
Portfolio Turnover, Rate 48.00%
MFS Total Return Bond Fund | Class A  
Prospectus [Line Items]  
Expenses Deferred Charges [Text Block] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.