Acquired Fund Fees And Expenses Over Assets Acquired (Underlying) Fund Fees and Expenses Amendment Flag Amendment Flag Annual Fund Operating Expenses Table [Text Block] Annual Fund Operating Expenses [Table] Bar Chart And Performance Table Heading Bar Chart and Performance Table [Heading] A C 000119415 [Member] A B C 000119416 [Member] B C C 000119417 [Member] C I C 000119418 [Member] I R1 C 000119419 [Member] R1 R2 C 000119420 [Member] R2 R3 C 000119421 [Member] R3 R4 C 000119422 [Member] R4 B C 000119423 [Member] B C C 000119424 [Member] C I C 000119425 [Member] I R1 C 000119426 [Member] R1 R2 C 000119427 [Member] R2 R3 C 000119428 [Member] R3 R4 C 000119429 [Member] R4 A C 000119430 [Member] A A C 000119431 [Member] A B C 000119432 [Member] B C C 000119433 [Member] C I C 000119434 [Member] I R1 C 000119435 [Member] R1 R2 C 000119436 [Member] R2 R3 C 000119437 [Member] R3 R4 C 000119438 [Member] R4 A C 000119439 [Member] A B C 000119440 [Member] B C C 000119441 [Member] C I C 000119442 [Member] I R1 C 000119443 [Member] R1 R2 C 000119444 [Member] R2 R3 C 000119445 [Member] R3 R4 C 000119446 [Member] R4 A C 000119447 [Member] A B C 000119448 [Member] B C C 000119449 [Member] C I C 000119450 [Member] I R1 C 000119451 [Member] R1 R2 C 000119452 [Member] R2 R3 C 000119453 [Member] R3 R4 C 000119454 [Member] R4 Distribution And Service 12 b 1 Fees Over Assets Distribution and/or Service (12b-1) Fees Document Creation Date Document Creation Date Document [Domain] Prospectus Document Effective Date Document Effective Date Document Information Document [Axis] Document [Axis] Document Period End Date Document Period End Date Document Type Document Type Entity Central Index Key Central Index Key Entity [Domain] Series Entity Registrant Name Registrant Name Expense Breakpoint Discounts Expense Breakpoint Discounts [Text] Expense Breakpoint Minimum Investment Required Amount Expense Breakpoint, Minimum Investment Required [Amount] Expense Example [Abstract] Expense Example: Expense Example By Year Caption Expense Example by, Year, Caption [Text] Expense Example By Year Column Name Expense Example, By Year, Column [Text] Expense Example Heading Expense Example [Heading] Expense Example Narrative [Text Block] Expense Example Narrative [Text Block] Expense Example No Redemption [Abstract] Expense Example, No Redemption: Expense Example No Redemption By Year Column Name Expense Example, No Redemption, By Year, Column [Text] Expense Example No Redemption Table [Text Block] Expense Example, No Redemption [Table] Expense Example No Redemption Year 01 Expense Example, No Redemption, 1 Year Expense Example No Redemption Year 03 Expense Example, No Redemption, 3 Years Expense Example With Redemption Table [Text Block] Expense Example, With Redemption [Table] Expense Example Year 01 Expense Example, with Redemption, 1 Year Expense Example Year 03 Expense Example, with Redemption, 3 Years Expense Heading Expense [Heading] Expense Narrative [Text Block] Expense Narrative [Text Block] Expenses Over Assets Total Annual Fund Operating Expenses Fee Waiver Or Reimbursement Over Assets Fee Reductions and/or Expense Reimbursements Fee Waiver Or Reimbursement Over Assets Date Of Termination Fee Waiver or Reimbursement over Assets, Date of Termination Legal Entity [Axis] Series [Axis] Management Fees Over Assets Management Fee Maximum Deferred Sales Charge Over Offering Price Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) Maximum Sales Charge Imposed On Purchases Over Offering Price Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) Net Expenses Over Assets Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements Objective Heading Objective [Heading] Objective Primary [Text Block] Objective, Primary [Text Block] Operating Expenses [Abstract] Operating Expenses: Operating Expenses Caption Operating Expenses Caption [Text] Operating Expenses Column Name Operating Expenses Column [Text] Other Expenses New Fund Based On Estimates Other Expenses, New Fund, Based on Estimates [Text] Other Expenses Over Assets Other Expenses Performance Narrative [Text Block] Performance Narrative [Text Block] Performance One Year Or Less Performance One Year or Less [Text] Portfolio Turnover Heading Portfolio Turnover [Heading] Portfolio Turnover [Text Block] Portfolio Turnover [Text Block] Prospectus Date ProspectusDate Prospectus Share Class [Axis] Share Class [Axis] Prospectus [Table] Prospectus: Risk Heading Risk [Heading] Risk Lose Money Risk Lose Money [Text] Risk Narrative [Text Block] Risk Narrative [Text Block] Risk Not Insured Depository Institution Risk Not Insured Depository Institution [Text] Risk Return [Abstract] Risk/Return: Risk Return Heading Risk/Return [Heading] MFS Lifetime 2015 Fund S 000038772 [Member] MFS Lifetime 2015 Fund MFS Lifetime 2025 Fund S 000038773 [Member] MFS Lifetime 2025 Fund MFS Lifetime 2035 Fund S 000038774 [Member] MFS Lifetime 2035 Fund MFS Lifetime 2045 Fund S 000038775 [Member] MFS Lifetime 2045 Fund MFS Lifetime 2055 Fund S 000038776 [Member] MFS Lifetime 2055 Fund Share Class [Domain] Share Classes Shareholder Fees [Abstract] Shareholder Fees: Shareholder Fees Caption Shareholder Fees Caption [Text] Shareholder Fees Column Name Shareholder Fees Column [Text] Shareholder Fees Table [Text Block] Shareholder Fees [Table] Strategy Heading Strategy [Heading] Strategy Narrative [Text Block] Strategy Narrative [Text Block] MFS Lifetime 2015 Fund (Prospectus Summary) Summary S 000038772 [Member] MFS Lifetime 2015 Fund (Prospectus Summary) MFS Lifetime 2025 Fund (Prospectus Summary) Summary S 000038773 [Member] MFS Lifetime 2025 Fund (Prospectus Summary) MFS Lifetime 2035 Fund (Prospectus Summary) Summary S 000038774 [Member] MFS Lifetime 2035 Fund (Prospectus Summary) MFS Lifetime 2045 Fund (Prospectus Summary) Summary S 000038775 [Member] MFS Lifetime 2045 Fund (Prospectus Summary) MFS Lifetime 2055 Fund (Prospectus Summary) Summary S 000038776 [Member] MFS Lifetime 2055 Fund (Prospectus Summary) Trading Symbol Trading Symbol