v3.26.1
Fees and Expenses
Apr. 30, 2026
USD ($)
MFS Core 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 Core Bond Fund
Class A
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%
Maximum Deferred Sales Charge (as a percentage of Offering Price) 1.00% [1] 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 Core Bond Fund
Class A
Class C
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Management Fees (as a percentage of Assets) 0.33% 0.33% 0.33% 0.33% 0.33% 0.33% 0.33% 0.33%
Distribution and Service (12b-1) Fees 0.25% 1.00% 0.00% 1.00% 0.50% 0.25% 0.00% 0.00%
Other Expenses (as a percentage of Assets): 1.03% 1.03% 1.03% 1.03% 1.03% 1.03% 1.03% 1.00%
Expenses (as a percentage of Assets) 1.61% 2.36% 1.36% 2.36% 1.86% 1.61% 1.36% 1.33%
Fee Waiver or Reimbursement [1] (0.97%) (0.97%) (0.97%) (0.97%) (0.97%) (0.97%) (0.97%) (1.00%)
Net Expenses (as a percentage of Assets) 0.64% 1.39% 0.39% 1.39% 0.89% 0.64% 0.39% 0.33%
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
[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 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 0.64% of the class' average daily net assets annually for each of Class A and Class R3 shares, 1.39% of the class' average daily net assets annually for each of Class C and Class R1 shares, 0.39% of the class' average daily net assets annually for each of Class I and Class R4 shares, 0.89% of the class' average daily net assets annually for Class R2 shares, and 0.33% 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 Core Bond Fund - USD ($)
Class A
Class C
 [1]
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Expense Example, with Redemption, 1 Year $ 488 $ 242 $ 40 $ 142 $ 91 $ 65 $ 40 $ 34
Expense Example, with Redemption, 3 Years 820 644 335 644 490 413 335 323
Expense Example, with Redemption, 5 Years 1,176 1,172 652 1,172 915 784 652 633
Expense Example, with Redemption, 10 Years $ 2,176 $ 2,433 $ 1,550 $ 2,622 $ 2,100 $ 1,829 $ 1,550 $ 1,514
[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 Core Bond Fund
Class C
USD ($)
 [1]
Expense Example, No Redemption, 1 Year $ 142
Expense Example, No Redemption, 3 Years 644
Expense Example, No Redemption, 5 Years 1,172
Expense Example, No Redemption, 10 Years $ 2,433
[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 110% of the average value of its portfolio (35% excluding to be announced (TBA) transactions).
Portfolio Turnover, Rate 110.00%
MFS Core 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 Lifetime Income 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 16 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 Lifetime Income 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 Lifetime Income 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) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
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): 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.08%
Acquired Fund Fees and Expenses 0.44% 0.44% 0.44% 0.44% 0.44% 0.44% 0.44% 0.44% 0.44%
Expenses (as a percentage of Assets) 0.88% 1.63% 1.63% 0.63% 1.63% 1.13% 0.88% 0.63% 0.52%
Fee Waiver or Reimbursement [1] (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.20%)
Net Expenses (as a percentage of Assets) 0.69% 1.44% 1.44% 0.44% 1.44% 0.94% 0.69% 0.44% 0.32%
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 bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.12)% 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 Lifetime Income 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 $ 492 $ 547 $ 247 $ 45 $ 147 $ 96 $ 70 $ 45 $ 33
Expense Example, with Redemption, 3 Years 676 796 496 183 496 340 262 183 147
Expense Example, with Redemption, 5 Years 874 1,069 869 332 869 604 469 332 271
Expense Example, with Redemption, 10 Years $ 1,446 $ 1,716 $ 1,716 $ 768 $ 1,917 $ 1,358 $ 1,067 $ 768 $ 633
[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 Lifetime Income Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 147 $ 147
Expense Example, No Redemption, 3 Years [1] 496 496
Expense Example, No Redemption, 5 Years [1] 869 869
Expense Example, No Redemption, 10 Years [1] $ 1,716 $ 1,716
[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 3% of the average value of its portfolio.
Portfolio Turnover, Rate 3.00%
MFS Lifetime Income 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 Lifetime 2030 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 16 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 Lifetime 2030 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) 5.75% 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 Lifetime 2030 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) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
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): 0.18% 0.18% 0.18% 0.18% 0.18% 0.18% 0.18% 0.18% 0.05%
Acquired Fund Fees and Expenses 0.46% 0.46% 0.46% 0.46% 0.46% 0.46% 0.46% 0.46% 0.46%
Expenses (as a percentage of Assets) 0.89% 1.64% 1.64% 0.64% 1.64% 1.14% 0.89% 0.64% 0.51%
Fee Waiver or Reimbursement [1] (0.18%) (0.18%) (0.18%) (0.18%) (0.18%) (0.18%) (0.18%) (0.18%) (0.19%)
Net Expenses (as a percentage of Assets) 0.71% 1.46% 1.46% 0.46% 1.46% 0.96% 0.71% 0.46% 0.32%
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 bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.14)% 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 Lifetime 2030 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 $ 643 $ 549 $ 249 $ 47 $ 149 $ 98 $ 73 $ 47 $ 33
Expense Example, with Redemption, 3 Years 826 800 500 187 500 344 266 187 144
Expense Example, with Redemption, 5 Years 1,023 1,075 875 339 875 610 475 339 266
Expense Example, with Redemption, 10 Years $ 1,592 $ 1,728 $ 1,728 $ 781 $ 1,929 $ 1,370 $ 1,080 $ 781 $ 622
[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 Lifetime 2030 Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 149 $ 149
Expense Example, No Redemption, 3 Years [1] 500 500
Expense Example, No Redemption, 5 Years [1] 875 875
Expense Example, No Redemption, 10 Years [1] $ 1,728 $ 1,728
[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 5% of the average value of its portfolio.
Portfolio Turnover, Rate 5.00%
MFS Lifetime 2030 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 Lifetime 2035 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 16 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 Lifetime 2035 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) 5.75% 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 Lifetime 2035 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) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
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): 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.05%
Acquired Fund Fees and Expenses 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50%
Expenses (as a percentage of Assets) 0.94% 1.69% 1.69% 0.69% 1.69% 1.19% 0.94% 0.69% 0.55%
Fee Waiver or Reimbursement [1] (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%)
Net Expenses (as a percentage of Assets) 0.75% 1.50% 1.50% 0.50% 1.50% 1.00% 0.75% 0.50% 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 bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.14)% 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 Lifetime 2035 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 $ 647 $ 553 $ 253 $ 51 $ 153 $ 102 $ 77 $ 51 $ 37
Expense Example, with Redemption, 3 Years 839 814 514 202 514 359 281 202 157
Expense Example, with Redemption, 5 Years 1,048 1,100 900 365 900 636 502 365 288
Expense Example, with Redemption, 10 Years $ 1,647 $ 1,782 $ 1,782 $ 841 $ 1,982 $ 1,426 $ 1,137 $ 841 $ 671
[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 Lifetime 2035 Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 153 $ 153
Expense Example, No Redemption, 3 Years [1] 514 514
Expense Example, No Redemption, 5 Years [1] 900 900
Expense Example, No Redemption, 10 Years [1] $ 1,782 $ 1,782
[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 11% of the average value of its portfolio.
Portfolio Turnover, Rate 11.00%
MFS Lifetime 2035 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 Lifetime 2040 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 16 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 Lifetime 2040 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) 5.75% 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 Lifetime 2040 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) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
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): 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.19% 0.05%
Acquired Fund Fees and Expenses 0.53% 0.53% 0.53% 0.53% 0.53% 0.53% 0.53% 0.53% 0.53%
Expenses (as a percentage of Assets) 0.97% 1.72% 1.72% 0.72% 1.72% 1.22% 0.97% 0.72% 0.58%
Fee Waiver or Reimbursement [1] (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%) (0.19%)
Net Expenses (as a percentage of Assets) 0.78% 1.53% 1.53% 0.53% 1.53% 1.03% 0.78% 0.53% 0.39%
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 bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.14)% 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 Lifetime 2040 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 $ 650 $ 556 $ 256 $ 54 $ 156 $ 105 $ 80 $ 54 $ 40
Expense Example, with Redemption, 3 Years 848 823 523 211 523 368 290 211 167
Expense Example, with Redemption, 5 Years 1,063 1,116 916 382 916 652 518 382 305
Expense Example, with Redemption, 10 Years $ 1,680 $ 1,815 $ 1,815 $ 877 $ 2,014 $ 1,461 $ 1,172 $ 877 $ 708
[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 Lifetime 2040 Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 156 $ 156
Expense Example, No Redemption, 3 Years [1] 523 523
Expense Example, No Redemption, 5 Years [1] 916 916
Expense Example, No Redemption, 10 Years [1] $ 1,815 $ 1,815
[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 8% of the average value of its portfolio.
Portfolio Turnover, Rate 8.00%
MFS Lifetime 2040 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 Lifetime 2045 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 16 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 Lifetime 2045 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) 5.75% 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 Lifetime 2045 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) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
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): 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% 0.06%
Acquired Fund Fees and Expenses 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54%
Expenses (as a percentage of Assets) 0.99% 1.74% 1.74% 0.74% 1.74% 1.24% 0.99% 0.74% 0.60%
Fee Waiver or Reimbursement [1] (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%)
Net Expenses (as a percentage of Assets) 0.79% 1.54% 1.54% 0.54% 1.54% 1.04% 0.79% 0.54% 0.40%
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 bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.14)% 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 Lifetime 2045 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 $ 651 $ 557 $ 257 $ 55 $ 157 $ 106 $ 81 $ 55 $ 41
Expense Example, with Redemption, 3 Years 853 829 529 216 529 374 295 216 172
Expense Example, with Redemption, 5 Years 1,072 1,125 925 392 925 662 528 392 315
Expense Example, with Redemption, 10 Years $ 1,701 $ 1,836 $ 1,836 $ 900 $ 2,035 $ 1,482 $ 1,195 $ 900 $ 731
[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 Lifetime 2045 Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 157 $ 157
Expense Example, No Redemption, 3 Years [1] 529 529
Expense Example, No Redemption, 5 Years [1] 925 925
Expense Example, No Redemption, 10 Years [1] $ 1,836 $ 1,836
[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 8% of the average value of its portfolio.
Portfolio Turnover, Rate 8.00%
MFS Lifetime 2045 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 Lifetime 2050 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 16 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 Lifetime 2050 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) 5.75% 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 Lifetime 2050 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) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
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): 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% 0.20% 0.06%
Acquired Fund Fees and Expenses 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54%
Expenses (as a percentage of Assets) 0.99% 1.74% 1.74% 0.74% 1.74% 1.24% 0.99% 0.74% 0.60%
Fee Waiver or Reimbursement [1] (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%) (0.20%)
Net Expenses (as a percentage of Assets) 0.79% 1.54% 1.54% 0.54% 1.54% 1.04% 0.79% 0.54% 0.40%
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 bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.14)% 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 Lifetime 2050 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 $ 651 $ 557 $ 257 $ 55 $ 157 $ 106 $ 81 $ 55 $ 41
Expense Example, with Redemption, 3 Years 853 829 529 216 529 374 295 216 172
Expense Example, with Redemption, 5 Years 1,072 1,125 925 392 925 662 528 392 315
Expense Example, with Redemption, 10 Years $ 1,701 $ 1,836 $ 1,836 $ 900 $ 2,035 $ 1,482 $ 1,195 $ 900 $ 731
[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 Lifetime 2050 Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 157 $ 157
Expense Example, No Redemption, 3 Years [1] 529 529
Expense Example, No Redemption, 5 Years [1] 925 925
Expense Example, No Redemption, 10 Years [1] $ 1,836 $ 1,836
[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 7% of the average value of its portfolio.
Portfolio Turnover, Rate 7.00%
MFS Lifetime 2050 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 Lifetime 2055 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. Expenses for Class B shares have been adjusted to reflect the full impact of the distribution fee.

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 16 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 Lifetime 2055 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) 5.75% 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 Lifetime 2055 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) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
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): 0.23% 0.23% 0.23% 0.23% 0.23% 0.23% 0.23% 0.23% 0.08%
Acquired Fund Fees and Expenses 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54%
Expenses (as a percentage of Assets) 1.02% 1.77% 1.77% 0.77% 1.77% 1.27% 1.02% 0.77% 0.62%
Fee Waiver or Reimbursement [1] (0.23%) (0.23%) (0.23%) (0.23%) (0.23%) (0.23%) (0.23%) (0.23%) (0.22%)
Net Expenses (as a percentage of Assets) 0.79% 1.54% 1.54% 0.54% 1.54% 1.04% 0.79% 0.54% 0.40%
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 bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.14)% 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 Lifetime 2055 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 $ 651 $ 557 $ 257 $ 55 $ 157 $ 106 $ 81 $ 55 $ 41
Expense Example, with Redemption, 3 Years 859 835 535 223 535 380 302 223 176
Expense Example, with Redemption, 5 Years 1,085 1,138 938 405 938 675 541 405 324
Expense Example, with Redemption, 10 Years $ 1,731 $ 1,867 $ 1,867 $ 933 $ 2,065 $ 1,514 $ 1,227 $ 933 $ 753
[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 Lifetime 2055 Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 157 $ 157
Expense Example, No Redemption, 3 Years [1] 535 535
Expense Example, No Redemption, 5 Years [1] 938 938
Expense Example, No Redemption, 10 Years [1] $ 1,867 $ 1,867
[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 10% of the average value of its portfolio.
Portfolio Turnover, Rate 10.00%
MFS Lifetime 2055 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 Lifetime 2060 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. Expenses for Class B and for Class R1 shares have been adjusted to reflect the full impact of the distribution fee.

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 16 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 Lifetime 2060 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) 5.75% 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 Lifetime 2060 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) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
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): 0.28% 0.28% 0.28% 0.28% 0.28% 0.28% 0.28% 0.28% 0.13%
Acquired Fund Fees and Expenses 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54%
Expenses (as a percentage of Assets) 1.07% 1.82% 1.82% 0.82% 1.82% 1.32% 1.07% 0.82% 0.67%
Fee Waiver or Reimbursement [1] (0.28%) (0.28%) (0.28%) (0.28%) (0.28%) (0.28%) (0.28%) (0.28%) (0.27%)
Net Expenses (as a percentage of Assets) 0.79% 1.54% 1.54% 0.54% 1.54% 1.04% 0.79% 0.54% 0.40%
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 bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.14)% 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 Lifetime 2060 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 $ 651 $ 557 $ 257 $ 55 $ 157 $ 106 $ 81 $ 55 $ 41
Expense Example, with Redemption, 3 Years 870 845 545 234 545 391 313 234 187
Expense Example, with Redemption, 5 Years 1,106 1,159 959 428 959 697 563 428 346
Expense Example, with Redemption, 10 Years $ 1,782 $ 1,917 $ 1,917 $ 988 $ 2,114 $ 1,566 $ 1,280 $ 988 $ 809
[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 Lifetime 2060 Fund - USD ($)
Class B
Class C
Expense Example, No Redemption, 1 Year [1] $ 157 $ 157
Expense Example, No Redemption, 3 Years [1] 545 545
Expense Example, No Redemption, 5 Years [1] 959 959
Expense Example, No Redemption, 10 Years [1] $ 1,917 $ 1,917
[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 15% of the average value of its portfolio.
Portfolio Turnover, Rate 15.00%
MFS Lifetime 2060 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 Lifetime 2065 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 16 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 Lifetime 2065 Fund
Class A
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) 5.75% 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] 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 Lifetime 2065 Fund
Class A
Class C
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Management Fees (as a percentage of Assets) 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Distribution and Service (12b-1) Fees 0.25% 1.00% 0.00% 1.00% 0.50% 0.25% 0.00% 0.00%
Other Expenses (as a percentage of Assets): 0.75% 0.75% 0.75% 0.75% 0.75% 0.75% 0.75% 0.60%
Acquired Fund Fees and Expenses 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54% 0.54%
Expenses (as a percentage of Assets) 1.54% 2.29% 1.29% 2.29% 1.79% 1.54% 1.29% 1.14%
Fee Waiver or Reimbursement [1] (0.75%) (0.75%) (0.75%) (0.75%) (0.75%) (0.75%) (0.75%) (0.74%)
Net Expenses (as a percentage of Assets) 0.79% 1.54% 0.54% 1.54% 1.04% 0.79% 0.54% 0.40%
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
[1] Massachusetts Financial Services Company (MFS) has agreed in writing to bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs, investment-related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles, or make payment to the fund, such that "Other Expenses" do not exceed 0.00% of the class' average daily net assets annually for each of Class A, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and (0.14)% 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 Lifetime 2065 Fund - USD ($)
Class A
Class C
 [1]
Class I
Class R1
Class R2
Class R3
Class R4
Class R6
Expense Example, with Redemption, 1 Year $ 651 $ 257 $ 55 $ 157 $ 106 $ 81 $ 55 $ 41
Expense Example, with Redemption, 3 Years 964 643 335 643 490 413 335 289
Expense Example, with Redemption, 5 Years 1,299 1,157 636 1,157 900 768 636 556
Expense Example, with Redemption, 10 Years $ 2,244 $ 2,378 $ 1,491 $ 2,568 $ 2,043 $ 1,771 $ 1,491 $ 1,320
[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 Lifetime 2065 Fund
Class C
USD ($)
 [1]
Expense Example, No Redemption, 1 Year $ 157
Expense Example, No Redemption, 3 Years 643
Expense Example, No Redemption, 5 Years 1,157
Expense Example, No Redemption, 10 Years $ 2,378
[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 21% of the average value of its portfolio.
Portfolio Turnover, Rate 21.00%
MFS Lifetime 2065 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.