Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Aug. 28, 2011
MFS Lifetime 2020 Fund (Prospectus Summary) | MFS Lifetime 2020 Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return, Heading	rr_RiskReturnHeading	Summary of Key Information
Investment Objective, Heading	rr_ObjectiveHeading	Investment Objective
investment Objective, Primary	rr_ObjectivePrimaryTextBlock	The fund's investment objective is to seek a high level of total return consistent with its asset allocation until the approximate retirement year in the fund's name; thereafter, the fund will seek total return through a combination of current income and capital appreciation. The asset allocation of the fund will change over time.
Expense, Heading	rr_ExpenseHeading	Fees and Expenses
Expense, Narrative	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay when you buy and hold shares of the fund. The annual fund operating expenses are based on expenses reported during the fund's most recently completed fiscal year and a weighted average of the total annual operating expenses (as reported in each underlying fund's most recent shareholder report) of, and the fee charged by (if any), the underlying funds in which the fund invested during the fund's most recently completed fiscal year, expressed as a percentage of the fund's average net assets during the period. They have been adjusted to reflect certain current fee arrangements. You may qualify for sales charge reductions if 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 or Reductions" on page 11 of the fund's prospectus and "Waivers of Sales Charges" on page 29 of the fund's statement of additional information Part I.
Shareholder Fees, Caption	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment):
Operating Expenses, Caption	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2012-08-31
Portfolio Turnover, Heading	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover	rr_PortfolioTurnoverTextBlock	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 19% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	19.00%
Expense Breakpoint, Discounts	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge reductions if 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	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 50,000
Expenses, Restated to Reflect Current	rr_ExpensesRestatedToReflectCurrent	They have been adjusted to reflect certain current fee arrangements.
Expense Example, Heading	rr_ExpenseExampleHeading	Example
Expense Example, Narrative	rr_ExpenseExampleNarrativeTextBlock	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	rr_ExpenseExampleByYearCaption	Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Investment Strategy, Heading	rr_StrategyHeading	Principal Investment Strategies
Investment Strategy, Narrative	rr_StrategyNarrativeTextBlock	The fund is designed to provide diversification among different asset classes by investing the majority of its assets in other MFS mutual funds, referred to as underlying funds. The underlying funds are selected following a two-stage asset allocation process. The first stage is a strategic asset allocation to establish the percentage of the fund's assets to be invested in the general asset classes of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an allocation to underlying funds that have less traditional investment strategies that MFS (Massachusetts Financial Services Company, the fund's investment adviser) believes provide diversification benefits when added to a portfolio consisting of stock and bond funds (referred to as Specialty Funds). The second stage involves the actual selection of underlying funds to represent the asset classes based on underlying fund classifications, historical risk, performance, and other factors. Within the stock fund allocations, MFS seeks to diversify globally (by including domestic and international underlying funds), in terms of market capitalization (by including large, mid, and small capitalization underlying funds) and by style (by including both growth and value underlying funds). Within the bond fund allocation, MFS includes underlying funds with varying degrees of interest rate and credit exposure. As of August 28, 2011, the fund's target allocation among asset classes and the underlying funds was: Bond Funds: 44% MFS Emerging Markets Debt Fund 3% MFS Global Bond Fund 5% MFS Government Securities Fund 10% MFS High Income Fund 5% MFS Inflation-Adjusted Bond Fund 6% MFS Limited Maturity Fund 2% MFS Research Bond Fund 13% Specialty Funds: 6% MFS Absolute Return Fund 1% MFS Commodity Strategy Fund 3% MFS Global Real Estate Fund 2% International Stock Funds: 12% MFS International Growth Fund 3% MFS International New Discovery Fund 1% MFS International Value Fund 3% MFS Research International Fund 6% U.S. Stock Funds: 39% MFS Growth Fund 8% MFS Mid Cap Growth Fund 7% MFS Mid Cap Value Fund 7% MFS New Discovery Fund 1% MFS New Discovery Value Fund 1% MFS Research Fund 8% MFS Value Fund 8% * The target asset class and underlying fund allocations presented in the table are rounded. The asset class allocations, as well as the underlying funds and their target weightings, are based on an allocation strategy designed for investors with the approximate retirement year in the fund's name. Investors should also consider their age, personal circumstances, risk tolerance, and overall investment strategy and allocation. The asset allocation strategy will become increasingly conservative over time. Upon reaching its stated target year, the fund's allocation strategy will be aligned with the allocation strategy of the MFS Lifetime Retirement Income Fund. It is expected that the fund will be combined with the MFS Lifetime Retirement Income Fund within five years of the date that its asset allocation strategy matches the asset allocation strategy of the MFS Lifetime Retirement Income Fund. The chart below illustrates how the asset allocation strategy of the fund will change over time. ASSET CLASS WEIGHTS FOR TARGET DATE FUNDS 71%Bond Funds 4% Specialty Funds 5% International Stock Funds 20% U.S. Stock Funds U.S. Stock Funds Years Before Target Date Target Date Years After Target Date 45 40 35 30 25 20 15 10 5 0 5 10 Asset class weight % 57% 57% 57% 57% 57% 54.5% 52% 41% 28% 20% 20% 20% International Stock Funds Years Before Target Date Target Date Years After Target Date 45 40 35 30 25 20 15 10 5 0 5 10 Asset class weight % 28% 28% 28% 28% 28% 24% 20% 13% 8% 5% 5% 5% Specialty Funds Years Before Target Date Target Date Years After Target Date 45 40 35 30 25 20 15 10 5 0 5 10 Asset class weight% 10% 10% 10% 10% 10% 9% 8% 6% 4% 4% 4% 4% Bond Funds Years Before Target Date Target Date Years After Target Date 45 40 35 30 25 20 15 10 5 0 5 10 Asset class weight% 5% 5% 5% 5% 5% 12.5% 20% 40% 60% 71% 71% 71% Investments for the underlying funds are selected primarily based on fundamental analysis of issuers. Quantitative analysis may also be considered.
Risk, Heading	rr_RiskHeading	Principal Risks
Risk, Narrative	rr_RiskNarrativeTextBlock	As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund, including near or after the target date. There is no guarantee that the fund will provide income at or through retirement. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. The principal risks of investing in the fund are: Stock Market/Company Risk: Stock markets are volatile and can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, and other conditions, as well as to investor perceptions of these conditions. The price of an equity security can decrease significantly in response to these conditions, and these conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the market in general. Foreign and Emerging Markets Risk: Exposure to foreign markets, especially emerging markets, through issuers or currencies can involve additional risks relating to market, economic, political, regulatory, geopolitical, or other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Emerging markets can have less developed markets and less developed legal, regulatory, and accounting systems, and greater political, social, and economic instability than developed markets. Currency Risk: The value of foreign currencies relative to the U.S. dollar fluctuates in response to market, economic, political, regulatory, geopolitical or other conditions, and a decline in the value of a foreign currency versus the U.S. dollar reduces the value in U.S. dollars of investments denominated in that foreign currency. Interest Rate Risk: The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes. Credit Risk: The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or underlying collateral and can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, or other conditions. Lower quality debt instruments (commonly referred to as "high yield securities" or "junk bonds") can involve a substantially greater risk of default or can already be in default, and their values can decline significantly. Lower quality debt instruments are regarded as having predominantly speculative characteristics. Lower quality debt instruments tend to be more sensitive to adverse news about the issuer, or the market or economy in general, than higher quality debt instruments. Prepayment/Extension Risk: Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument's holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended. Inflation-Adjusting Risk: Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline. Municipal Risk: The price of a municipal instrument can be volatile and significantly affected by adverse tax or court rulings, legislative or political changes, changes in specific or general market and economic conditions, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in these industries can significantly affect the fund and the overall municipal market. Real Estate-Related Investment Risk: The risks of investing in real estate-related securities include certain risks associated with the direct ownership of real estate and the real estate industry in general. These include risks related to general, regional and local economic conditions; fluctuations in interest rates; property tax rates, zoning laws, environmental regulations and other governmental action; cash flow dependency; increased operating expenses; lack of availability of mortgage funds; losses due to natural disasters; changes in property values and rental rates; and other factors. The securities of smaller real estate-related issuers can be more volatile, less liquid, and have more limited financial resources than securities of larger issuers. Commodity Risk: The value of commodities may be more volatile than the value of equity securities or debt instruments and their value may be affected by changes in overall market movements, commodity index volatility, changes in interest rates, or factors affecting a particular industry or commodity. The price of a commodity may be affected by demand/supply imbalances in the market for the commodity. Derivatives Risk: Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives' original cost. Derivatives can involve leverage. Investment Selection and Allocation Risk: MFS' analysis of an investment and its assessment of the mix of general risk and return characteristics of asset classes and underlying funds can be incorrect and can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or funds that invest in similar asset classes. Counterparty and Third Party Risk: Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty's or third party's ability to perform in accordance with the terms of the transaction. Liquidity Risk: It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.
Risk, Lose Money	rr_RiskLoseMoney	As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund, including near or after the target date.
Risk, Not Insured Depository Institution	rr_RiskNotInsuredDepositoryInstitution	An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table, Heading	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance, Narrative	rr_PerformanceNarrativeTextBlock	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance and one or more other measures of performance for markets in which the fund may invest. The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance, Information Illustrates Variability of Returns	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance and one or more other measures of performance for markets in which the fund may invest.
Performance, Additional Market Index	rr_PerformanceAdditionalMarketIndex	The MFS Lifetime 2020 Fund Blended Index composed at period end of the following amounts of the following indices: Barclays Capital U.S. Aggregate Bond Index (42%); Standard & Poor's 500 Stock Index (41%); MSCI EAFE (Europe, Australasia, Far East) Index (13%); Dow Jones-UBS Commodity Index (3%); and FTSE EPRA/NAREIT Developed Real Estate Index (2%).
Performance, Availability Phone Number	rr_PerformanceAvailabilityPhone	1-800-225-2606
Performance, Availability Website Address	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance, Past Does Not Indicate Future	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Bar Chart, Heading	rr_BarChartHeading	Class A Bar Chart.
Bar Chart, Narrative	rr_BarChartNarrativeTextBlock	The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart, Does Not Reflect Sales Loads	rr_BarChartDoesNotReflectSalesLoads	The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart, Closing	rr_BarChartClosingTextBlock	The total return for the six-month period ended June 30, 2011 was 4.67%. During the period(s) shown in the bar chart, the highest quarterly return was 14.17% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (17.23)% (for the calendar quarter ended December 31, 2008).
Performance Table, Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Performance Table, Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table, Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table, One Class of after Tax Shown	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns are shown for only one of the fund's classes of shares, and after-tax returns for the fund's other classes of shares will vary from the returns shown.
Performance Table, Closing	rr_PerformanceTableClosingTextBlock	After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns are shown for only one of the fund's classes of shares, and after-tax returns for the fund's other classes of shares will vary from the returns shown.
Average Annual Returns, Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2010)
MFS Lifetime 2020 Fund (Prospectus Summary) | MFS Lifetime 2020 Fund | A
Risk/Return:	rr_RiskReturnAbstract
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the six-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2011
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	4.67%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	14.17%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(17.23%)
MFS Lifetime 2020 Fund | Standard & Poor's 500 Stock Index
Risk/Return:	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	15.06%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	2.29%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	2.76%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | MFS Lifetime 2020 Fund Blended Index
Risk/Return:	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Lifetime 2020 Fund Blended Index	[1]
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	11.35%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	3.94%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	4.29%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | A
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees, Column Name	rr_ShareholderFeesColumnName	A
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%	[2]
Operating Expenses, Column Name	rr_OperatingExpensesColumnName	A
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.25%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.19%)	[3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.06%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	677
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	931
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	1,205
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	1,984
Annual Return 2006	rr_AnnualReturn2006	12.39%
Annual Return 2007	rr_AnnualReturn2007	8.91%
Annual Return 2008	rr_AnnualReturn2008	(29.79%)
Annual Return 2009	rr_AnnualReturn2009	27.28%
Annual Return 2010	rr_AnnualReturn2010	14.25%
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	A Shares Returns Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	7.68%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	3.33%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	3.79%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | A | After Taxes on Distributions
Risk/Return:	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	A Shares Returns After Taxes on Distributions
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	7.02%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	2.54%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	2.94%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | A | After Taxes on Distributions and Sales
Risk/Return:	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	A Shares Returns After Taxes on Distributions and Sale of Fund Shares
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	5.11%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	2.49%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	2.84%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | B
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees, Column Name	rr_ShareholderFeesColumnName	B
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	4.00%
Operating Expenses, Column Name	rr_OperatingExpensesColumnName	B
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.00%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.19%)	[3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.81%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	584
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	909
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	1,260
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	2,118
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	184
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	609
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	1,060
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	2,118
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	B Shares Returns Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	9.44%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	3.50%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	4.08%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | C
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees, Column Name	rr_ShareholderFeesColumnName	C
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Operating Expenses, Column Name	rr_OperatingExpensesColumnName	C
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.00%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.19%)	[3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.81%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	284
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	609
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	1,060
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	2,312
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	184
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	609
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	1,060
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	2,312
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	C Shares Returns Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	12.46%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	3.86%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	4.25%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | I
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees, Column Name	rr_ShareholderFeesColumnName	I
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses, Column Name	rr_OperatingExpensesColumnName	I
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.00%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.19%)	[3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.81%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	83
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	300
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	534
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	1,207
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	I Shares Returns Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	14.66%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	4.90%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	5.30%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | R1
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees, Column Name	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses, Column Name	rr_OperatingExpensesColumnName	R1
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.00%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.19%)	[3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.81%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	184
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	609
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	1,060
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	2,312
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	R1 Shares Returns Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	13.48%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	3.82%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	4.21%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005
MFS Lifetime 2020 Fund | R2
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees, Column Name	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses, Column Name	rr_OperatingExpensesColumnName	R2
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.50%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.19%)	[3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.31%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	133
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	455
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	800
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	1,774
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	R2 Shares Returns Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	14.08%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	4.31%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	4.72%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 26, 2005
MFS Lifetime 2020 Fund | R3
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees, Column Name	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses, Column Name	rr_OperatingExpensesColumnName	R3
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.25%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.19%)	[3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.06%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	108
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	378
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	668
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	1,495
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	R3 Shares Returns Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	14.34%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	4.57%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	4.98%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 26, 2005
MFS Lifetime 2020 Fund | R4
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees, Column Name	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses, Column Name	rr_OperatingExpensesColumnName	R4
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.19%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.00%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.19%)	[3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.81%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	83
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	300
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	534
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	$ 1,207
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	R4 Shares Returns Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	14.67%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	4.86%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	5.26%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Sep. 29, 2005

[1] The MFS Lifetime 2020 Fund Blended Index composed at period end of the following amounts of the following indices: Barclays Capital U.S. Aggregate Bond Index (42%); Standard & Poor's 500 Stock Index (41%); MSCI EAFE (Europe, Australasia, Far East) Index (13%); Dow Jones-UBS Commodity Index (3%); and FTSE EPRA/NAREIT Developed Real Estate Index (2%).

[2] On shares purchased without an initial sales charge and redeemed within 24 months of purchase.

[3] MFS agreed in writing to bear the fund's expenses, excluding management fees, distribution and service fees, interest, taxes, extraordinary expenses, brokerage and transaction costs and investment-related expenses and including fees and expenses associated with investments in investment companies and other similar investment vehicles, such that "Other Expenses" do not exceed 0.00% of the fund's average daily net assets annually for each class of shares. This agreement will continue until at least August 31, 2012, after which MFS may increase such expense limitation to 0.10% of the fund's average daily net assets annually for each class of shares without a vote of the fund's Board of Trustees. Any increase above 0.10% would require a vote of the fund's Board of Trustees.