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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MFS® Conservative Allocation Fund - Summary of Key Information
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The investment objective of the fund is to seek a high level of total return consistent with a conservative level of risk relative to the other MFS Asset Allocation Funds.  (The MFS Asset Allocation Funds currently include the MFS Conservative Allocation Fund, MFS Moderate Allocation Fund, MFS Growth Allocation Fund, and MFS Aggressive Growth Allocation Fund.)

Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay when you buy and hold shares of the fund.


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 H-1 of the fund’s Statement of Additional Information (“SAI”).

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment):
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] 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 5% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 5.00%
Expense Breakpoint Discounts [Text] 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
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] 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 [Text] rr_ExpenseExampleByYearCaption Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The fund is designed to provide diversification among different asset classes by investing its assets in other mutual funds advised by MFS (Massachusetts Financial Services Company, the fund’s investment adviser), 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 determine 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 believes provide diversification benefits when added to a portfolio consisting of stock and bond funds (referred to as Specialty Funds) based on the risk/return potential of the different asset classes and the risk profile of the fund. 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 September 1, 2013, the fund’s target allocation among asset classes and the underlying funds was:


Bond Funds:

 

60

%

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

 

10

%

MFS Limited Maturity Fund

 

10

%

MFS Research Bond Fund

 

17

%

International Stock Funds:

 

8

%

MFS International Growth Fund

 

2

%

MFS International Value Fund

 

2

%

MFS Research International Fund

 

4

%

U.S. Stock Funds:

 

28

%

MFS Growth Fund

 

6

%

MFS Mid Cap Growth Fund

 

4

%

MFS Mid Cap Value Fund

 

4

%

MFS New Discovery Fund

 

1

%

MFS New Discovery Value Fund

 

1

%

MFS Research Fund

 

6

%

MFS Value Fund

 

6

%

Specialty Funds:

 

4

%

MFS Absolute Return Fund

 

2

%

MFS Commodity Strategy Fund

 

1

%

MFS Global Real Estate Fund

 

1

%


Due to rounding, the target asset class and underlying fund allocations presented in the table may not total 100%.

Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] 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. 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:


Investment Selection and Allocation Risk:  MFS’ investment analysis, its selection of investments, and its assessment of the risk/return potential of asset classes and underlying funds may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.


Underlying Funds Risk:  MFS’ strategy of investing in underlying funds exposes the fund to the risks of the underlying funds. Each underlying fund pursues its own investment objective and strategies and may not achieve its objective.


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 or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, and 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.


Foreign and Emerging Markets Risk:  Exposure to foreign markets, especially emerging markets, through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and 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, greater custody and operational risk, 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, industry, political, regulatory, geopolitical, and 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.


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-Adjusted Debt Instruments 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.


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.


Growth Company Risk:  The stocks of growth companies can be more sensitive to the company’s earnings and more volatile than the market in general.


Value Company Risk:  The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general.


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 and property tax rates; shifts in 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; overbuilding; losses due to casualty or condemnation; changes in property values and rental rates; and other factors.  The securities of smaller real estate-related issuers can be more volatile and less liquid than securities of larger issuers and their issuers can have more limited financial resources.


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.


Leveraging Risk:  Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.


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 [Text] 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.
Risk Not Insured Depository Institution [Text] 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 [Text Block] 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 [Text] 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 [Text] rr_PerformanceAdditionalMarketIndex As of December 31, 2012, the MFS Conservative Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: 28% Standard & Poor's 500 Stock Index; 8% MSCI EAFE (Europe, Australasia, Far East) Index; 1% The Dow Jones-UBS Commodity Index; 1% FTSE EPRA/NAREIT Developed Real Estate Index; and 62% Barclays U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the period, and may differ in the future.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-225-2606
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress mfs.com
Performance Past Does Not Indicate Future [Text] 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 [Text Block] 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 [Text] 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 [Text Block] rr_BarChartClosingTextBlock

The total return for the six-month period ended June 30, 2013 was 2.04%. During the period(s) shown in the bar chart, the highest quarterly return was 10.76% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (9.28)% (for the calendar quarter ended December 31, 2008).

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, 2013
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 2.04%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 10.76%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (9.28%)
Performance Table Heading rr_PerformanceTableHeading Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text] 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 [Text] 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 [Text Block] 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.

Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (for the Periods Ended December 31, 2012)
Barclays U.S. Aggregate Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Aggregate Bond Index
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 4.21%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.95%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.18%
MFS Conservative Allocation Fund Blended Index
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Conservative Allocation Fund Blended Index
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 8.86% [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.24% [1]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.16% [1]
A
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther 1.00% [2]
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.07%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.99%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.99%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 670
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 872
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,091
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,718
Annual Return 2003 rr_AnnualReturn2003 11.65%
Annual Return 2004 rr_AnnualReturn2004 7.23%
Annual Return 2005 rr_AnnualReturn2005 3.94%
Annual Return 2006 rr_AnnualReturn2006 8.65%
Annual Return 2007 rr_AnnualReturn2007 7.33%
Annual Return 2008 rr_AnnualReturn2008 (16.60%)
Annual Return 2009 rr_AnnualReturn2009 22.15%
Annual Return 2010 rr_AnnualReturn2010 11.29%
Annual Return 2011 rr_AnnualReturn2011 2.43%
Annual Return 2012 rr_AnnualReturn2012 10.65%
Label rr_AverageAnnualReturnLabel A Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 4.29%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.90%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.80%
A | After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel A Shares Returns After Taxes on Distributions
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 3.59%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 2.97%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 4.88%
A | After Taxes on Distributions and Sale of Fund Shares
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel A Shares Returns After Taxes on Distributions and Sale of Fund Shares
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 2.88%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 2.81%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 4.54%
B
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther 4.00%
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.07%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.74%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.74%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 577
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 848
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,144
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,853
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 177
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 548
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 944
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 1,853
Label rr_AverageAnnualReturnLabel B Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.80%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.04%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.85%
C
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther 1.00%
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.07%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.74%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.74%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 277
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 548
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 944
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,052
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 177
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 548
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 944
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 2,052
Label rr_AverageAnnualReturnLabel C Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 8.82%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.39%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.70%
I
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.07%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.74%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.74%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 76
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 237
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 411
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 918
Label rr_AverageAnnualReturnLabel I Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 10.92%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.42%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.75%
529A
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.09%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.05%) [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.04%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2014-09-30
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 675
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 897
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,137
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,823
Label rr_AverageAnnualReturnLabel 529A Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 4.20%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.81%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.62%
529B
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther 4.00%
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.84%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.05%) [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.79%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2014-09-30
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 582
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 874
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,191
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,958
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 182
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 574
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 991
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 1,958
Label rr_AverageAnnualReturnLabel 529B Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.67%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.93%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.66%
529C
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther 1.00%
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.17%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.84%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.05%) [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.79%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2014-09-30
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 282
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 574
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 991
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,154
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 182
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 574
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 991
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 2,154
Label rr_AverageAnnualReturnLabel 529C Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 8.75%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.30%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.52%
R1
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.07%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.74%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.74%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 177
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 548
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 944
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,052
Label rr_AverageAnnualReturnLabel R1 Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 9.82%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.38%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.62%
R2
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.07%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.24%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 1.24%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 126
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 393
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 681
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,500
Label rr_AverageAnnualReturnLabel R2 Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 10.30%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.89%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.11%
R3
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.07%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.99%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 315
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 547
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,213
Label rr_AverageAnnualReturnLabel R3 Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 10.65%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.16%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.41%
R4
  
Risk/Return: rr_RiskReturnAbstract  
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_MaximumDeferredSalesChargeOverOther none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.07%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.67%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.74%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [3]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.74%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 76
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 237
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 411
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 918
Label rr_AverageAnnualReturnLabel R4 Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 10.91%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.45%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.71%
[1] As of December 31, 2012, the MFS Conservative Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: 28% Standard & Poor's 500 Stock Index; 8% MSCI EAFE (Europe, Australasia, Far East) Index; 1% The Dow Jones-UBS Commodity Index; 1% FTSE EPRA/NAREIT Developed Real Estate Index; and 62% Barclays U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the period, and may differ in the future.
[2] On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.
[3] MFS Fund Distributors, Inc., has agreed in writing to waive the program management fee for each of the fund's Class 529A, Class 529B, and Class 529C shares to 0.05% of the fund's average daily net assets attributable to each share class annually. This written agreement will expire on September 30, 2014, unless MFS Fund Distributors, Inc., elects to extend the waiver.