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Label Element Value
MFS Conservative Allocation Fund  
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 fund’s investment objective 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 are 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. Investors may also pay commissions or other fees to their financial intermediaries when they buy and hold shares of the fund, which are not reflected below. Expenses for Class 529B 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 or Class 529A 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 14 and “Appendix A – Waivers and Reductions of Sales Charges” on page A-1 of the fund’s prospectus.

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 12% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 12.00%
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 invested in the general asset classes of (1) Bond Funds, (2) International Stock Funds, and (3) U.S. Stock Funds, as well as (4) Specialty Funds (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) 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 by geography (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 geographic, interest rate and credit exposure.

 

MFS normally invests the underlying funds’ assets across different industries, sectors, countries, and regions, but MFS may invest a significant percentage of the underlying funds’ assets in issuers in a single industry, sector, country, or region.

 

As of September 1, 2020, the fund’s approximate target allocation among asset classes and the underlying funds was:

 

Bond Funds:

 

60.0

%

MFS Emerging Markets Debt Fund

 

3.0

%

MFS Emerging Markets Debt Local Currency Fund

 

2.0

%

MFS Global Bond Fund

 

5.0

%

MFS Government Securities Fund

 

10.0

%

MFS High Income Fund

 

5.0

%

MFS Inflation-Adjusted Bond Fund

 

10.0

%

MFS Limited Maturity Fund

 

10.0

%

MFS Total Return Bond Fund

 

15.0

%

International Stock Funds:

 

8.0

%

MFS International Growth Fund

 

2.0

%

MFS International Intrinsic Value Fund

 

2.0

%

MFS Research International Fund

 

4.0

%

U.S. Stock Funds:

 

28.0

%

MFS Growth Fund

 

6.0

%

MFS Mid Cap Growth Fund

 

4.0

%

MFS Mid Cap Value Fund

 

4.0

%

MFS New Discovery Fund

 

1.0

%

MFS New Discovery Value Fund

 

1.0

%

MFS Research Fund

 

6.0

%

MFS Value Fund

 

6.0

%

Specialty Funds:

 

4.0

%

MFS Commodity Strategy Fund

 

2.0

%

MFS Global Real Estate Fund

 

2.0

%

 

All percentages are rounded to the nearest tenth of a percent.  As a result, the sum of the target underlying fund allocations in each asset class may not equal the target asset class allocations for such asset class, and 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:

 

Allocation Risk:  MFS’ assessment of the risk/return potential of asset classes and underlying funds, and the resulting allocation among 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.  In addition, shareholders of the fund will indirectly bear the fees and expenses of the underlying funds.

 

Investment Selection Risk:  MFS’ investment analysis and its selection of investments 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.

 

Debt Market Risk:  Debt markets can be volatile and can decline significantly in response to, or investor perceptions of, issuer, market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions.  These conditions can affect a single instrument, issuer, or borrower, a particular type of instrument, issuer, or borrower, a segment of the debt markets or the debt markets generally. Certain events can have a dramatic adverse effect on debt markets and may lead to periods of high volatility and reduced liquidity in a debt market or segment of a debt market.

 

Interest Rate Risk:  In general, the price of a debt instrument falls when interest rates rise and rises when interest rates fall. Interest rate risk is generally greater for instruments with longer maturities, or that do not pay current interest.

 

Credit Risk:  The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or other entity responsible for payment, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in, or perceptions of, the financial condition of the issuer, borrower, counterparty, or other entity, or underlying collateral or assets, or changes in, or perceptions of, specific or general market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions.

 

Below investment grade 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. Below investment grade quality debt instruments are regarded as having predominantly speculative characteristics. Below investment grade 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-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 changes or court rulings, legislative or political changes, changes in specific or general market and economic conditions and developments, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in certain industries can significantly affect the fund and  

the overall municipal market.  Municipal instruments may be more susceptible to downgrades or defaults during economic downturns or similar periods of economic stress, which in turn could affect the market values and marketability of many or all municipal obligations of issuers in a state, U.S. territory, or possession. For example, the novel coronavirus (COVID-19) pandemic has significantly stressed the financial resources of many municipal issuers, which may impair a municipal issuer’s ability to meet its financial obligations when due and could adversely impact the value of its bonds, which could negatively impact the performance of the fund.

 

Equity Market Risk/Company Risk:  Equity markets are volatile and can decline significantly in response to, or investor perceptions of, issuer, market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions.  These conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the equity markets in general.  Certain events can have a dramatic adverse effect on equity markets and may lead to periods of high volatility in an equity market or a segment of an equity market.

 

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.

 

Intrinsic Value Strategy Risk:  The stocks of companies that MFS believes are undervalued compared to their intrinsic value can continue to be undervalued for long periods of time, may not realize their expected value, and can be volatile.

 

Focus Risk:  Issuers in a single industry, sector, country, or region can react similarly to market, currency, political, economic, regulatory, geopolitical, environmental, public health, and other conditions, and the fund’s performance will be affected by the conditions in the industries, sectors, countries and regions to which the fund is exposed.

 

Foreign Risk:  Exposure to foreign markets through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. These factors can make foreign investments, especially those tied economically to 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 Risk:  Investments tied economically to emerging markets, especially frontier markets, can involve additional and greater risks than the risks associated with investments in developed foreign markets.  Emerging markets can have less developed markets, greater custody and operational risk, less developed legal, regulatory, and accounting systems, and greater political, social, geopolitical, 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, environmental, public health, and other conditions, and changes in currency exchange rates impact the financial condition of companies or other issuers and may change the value in U.S. dollars of investments denominated in foreign currencies.

 

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; difficulties in valuing and disposing of real estate; 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; the management skill and creditworthiness of the real estate investment trust (REIT) manager; 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.

 

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 or willingness to perform in accordance with the terms of the transaction.

 

Liquidity Risk:  It may be difficult to value, and it may not be possible to sell, certain investments, types of investments, and/or investments in certain segments of the market, and the fund may have to sell certain of these investments at prices or times that are not advantageous in order to meet redemptions or other cash needs.

 

Large Shareholder Risk: From time to time, shareholders of the fund (which may include institutional investors, financial intermediaries, or other MFS funds) may make relatively large redemptions or purchases of fund shares.  These transactions may cause the fund to sell securities or invest additional cash, as the case may be, at disadvantageous prices.  Redemptions of a large number of shares also may increase transaction costs or have adverse tax consequences for shareholders of the fund by requiring a sale of portfolio securities.

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 [Text] rr_RiskNotInsured 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, 2019, 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; 2% Bloomberg Commodity Index; 2% FTSE EPRA Nareit Developed Real Estate Index; and 60% Bloomberg Barclays U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods, 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, 2020, was 0.43%. During the period(s) shown in the bar chart, the highest quarterly return was 7.67% (for the calendar quarter ended March 31, 2019) and the lowest quarterly return was (5.59)% (for the calendar quarter ended September 30, 2011).

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, 2020
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.43%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 7.67%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (5.59%)
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 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

As of December 31, 2019, 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; 2% Bloomberg Commodity Index; 2% FTSE EPRA Nareit Developed Real Estate Index; and 60% Bloomberg Barclays U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods, and may differ in the future.

 

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-advantaged 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 Return, Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (For the Periods Ended December 31, 2019)
MFS Conservative Allocation Fund | Bloomberg Barclays U.S. Aggregate Bond Index  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 8.72%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.05%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 3.75%
MFS Conservative Allocation Fund | MFS Conservative Allocation Fund Blended Index  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 16.26%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.77%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.78%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [1]
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.08%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.89%
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge reductions if, with respect to Class A or Class 529A 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] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 661
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 843
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,040
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,608
Annual Return 2010 rr_AnnualReturn2010 11.29%
Annual Return 2011 rr_AnnualReturn2011 2.43%
Annual Return 2012 rr_AnnualReturn2012 10.65%
Annual Return 2013 rr_AnnualReturn2013 8.72%
Annual Return 2014 rr_AnnualReturn2014 3.94%
Annual Return 2015 rr_AnnualReturn2015 (0.78%)
Annual Return 2016 rr_AnnualReturn2016 5.42%
Annual Return 2017 rr_AnnualReturn2017 10.78%
Annual Return 2018 rr_AnnualReturn2018 (3.10%)
Annual Return 2019 rr_AnnualReturn2019 17.09%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 10.36%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.38%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.85%
MFS Conservative Allocation Fund | A | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 9.12%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.23%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 4.86%
MFS Conservative Allocation Fund | A | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 6.40%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.03%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 4.31%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice 4.00%
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.08%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.64%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 567
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 817
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,092
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,743
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 167
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 517
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 892
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,743
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 12.19%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.49%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.84%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice 1.00%
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.08%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.64%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 267
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 517
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 892
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,944
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 167
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 517
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 892
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,944
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 15.20%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.83%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.69%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.08%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.64%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 65
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 205
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 357
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 798
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 17.36%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.89%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.75%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.08%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.64%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 167
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 517
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 892
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,944
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 16.22%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.83%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.68%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.08%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.14%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 116
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 362
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 628
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,386
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 16.82%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.36%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.22%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.08%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.89%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 91
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 284
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 493
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,096
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 17.02%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.62%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.47%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.08%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.64%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 65
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 205
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 357
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 798
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 17.38%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.89%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.75%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.13%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.94%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge reductions if, with respect to Class A or Class 529A 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] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 665
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 857
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,065
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,663
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 10.35%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.35%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.80%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice 4.00%
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.13%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.69%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 572
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 833
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,118
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,799
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 172
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 533
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 918
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,799
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 12.15%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.46%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.79%
MFS Conservative Allocation Fund | 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_MaximumDeferredSalesChargeOverOfferingPrice 1.00%
Management Fee rr_ManagementFeesOverAssets none
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.13%
Acquired (Underlying) Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.56%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.69%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 272
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 533
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 918
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,998
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 172
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 533
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 918
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,998
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 15.20%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.78%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.63%
[1] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.