S 000002506 Summary1 [Member]
Prospectus Summary
Prospectus Summary
S 000002506 [Member]
MFS Aggressive Growth Allocation Fund
MFS Aggressive Growth Allocation Fund
C 000006838 [Member]
Class A
Class A
C 000006843 [Member]
Class B
Class B
C 000006844 [Member]
Class C
Class C
C 000006845 [Member]
Class I
Class I
C 000006847 [Member]
Class R1
Class R1
C 000006849 [Member]
Class R2
Class R2
C 000006850 [Member]
Class R3
Class R3
C 000006839 [Member]
Class R4
Class R4
C 000231058 [Member]
Class R6
Class R6
cik0000783740_PrincipalRisks2Member [Member]
Principal Risks
Principal Risks
cik0000783740_AllocationRisk2Member [Member]
Allocation Risk
Allocation Risk
cik0000783740_UnderlyingFundsRisk2Member [Member]
Underlying Funds Risk
Underlying Funds Risk
cik0000783740_InvestmentSelectionRisk2Member [Member]
Investment Selection Risk
Investment Selection Risk
cik0000783740_EquityMarketRiskCompanyRisk2Member [Member]
Equity Market Risk/Company Risk
Equity Market Risk/Company Risk
cik0000783740_GrowthCompanyRisk2Member [Member]
Growth Company Risk
Growth Company Risk
cik0000783740_ValueCompanyRisk2Member [Member]
Value Company Risk
Value Company Risk
cik0000783740_DebtMarketRisk2Member [Member]
Debt Market Risk
Debt Market Risk
cik0000783740_InterestRateRisk2Member [Member]
Interest Rate Risk
Interest Rate Risk
cik0000783740_CreditRisk2Member [Member]
Credit Risk
Credit Risk
cik0000783740_PrepaymentExtensionRisk2Member [Member]
Prepayment/Extension Risk
Prepayment/Extension Risk
cik0000783740_Inflation-AdjustedDebtInstrumentsRisk2Member [Member]
Inflation-Adjusted Debt Instruments Risk
Inflation-Adjusted Debt Instruments Risk
cik0000783740_FocusRisk2Member [Member]
Focus Risk
Focus Risk
cik0000783740_ForeignRisk2Member [Member]
Foreign Risk
Foreign Risk
cik0000783740_EmergingMarketsRisk2Member [Member]
Emerging Markets Risk
Emerging Markets Risk
cik0000783740_CurrencyRisk2Member [Member]
Currency Risk
Currency Risk
cik0000783740_RealEstate-RelatedInvestmentRisk2Member [Member]
Real Estate-Related Investment Risk
Real Estate-Related Investment Risk
cik0000783740_Commodity-RelatedInvestmentsRisk2Member [Member]
Commodity-Related Investments Risk
Commodity-Related Investments Risk
cik0000783740_When-IssuedDelayedDeliveryandForwardCommitmentTransactionRisk2Member [Member]
When-Issued, Delayed Delivery, and Forward Commitment Transaction Risk
When-Issued, Delayed Delivery, and Forward Commitment Transaction Risk
cik0000783740_DerivativesRisk2Member [Member]
Derivatives Risk
Derivatives Risk
cik0000783740_LeveragingRisk2Member [Member]
Leveraging Risk
Leveraging Risk
cik0000783740_CounterpartyandThirdPartyRisk2Member [Member]
Counterparty and Third Party Risk
Counterparty and Third Party Risk
cik0000783740_LiquidityRisk2Member [Member]
Liquidity Risk
Liquidity Risk
cik0000783740_LargeShareholderRisk2Member [Member]
Large Shareholder Risk
Large Shareholder Risk
cik0000783740_StandardPoors500StockIndex31Member [Member]
Standard & Poor's 500 Stock Index
Standard & Poor's 500 Stock Index
cik0000783740_MFSAggressiveGrowthAllocationFundBlendedIndex32Member [Member]
MFS Aggressive Growth Allocation Fund Blended Index
MFS Aggressive Growth Allocation Fund Blended Index
S 000050658 Summary2 [Member]
Prospectus Summary
Prospectus Summary
S 000050658 [Member]
MFS Blended Research Growth Equity Fund
MFS Blended Research Growth Equity Fund
C 000160020 [Member]
Class A
Class A
C 000160021 [Member]
Class B
Class B
C 000160022 [Member]
Class C
Class C
C 000160023 [Member]
Class I
Class I
C 000160024 [Member]
Class R1
Class R1
C 000160025 [Member]
Class R2
Class R2
C 000160026 [Member]
Class R3
Class R3
C 000160027 [Member]
Class R4
Class R4
C 000160028 [Member]
Class R6
Class R6
cik0000783740_InvestmentStrategyRisk2Member [Member]
Investment Strategy Risk
Investment Strategy Risk
cik0000783740_Non-DiversificationRisk2Member [Member]
Non-Diversification Risk
Non-Diversification Risk
cik0000783740_Russell3000Index33Member [Member]
Russell 3000® Index
Russell 3000® Index
cik0000783740_Russell1000GrowthIndex34Member [Member]
Russell 1000® Growth Index
Russell 1000® Growth Index
S 000050659 Summary3 [Member]
Prospectus Summary
Prospectus Summary
S 000050659 [Member]
MFS Blended Research Small Cap Equity Fund
MFS Blended Research Small Cap Equity Fund
C 000160029 [Member]
Class A
Class A
C 000160030 [Member]
Class B
Class B
C 000160031 [Member]
Class C
Class C
C 000160032 [Member]
Class I
Class I
C 000160033 [Member]
Class R1
Class R1
C 000160034 [Member]
Class R2
Class R2
C 000160035 [Member]
Class R3
Class R3
C 000160036 [Member]
Class R4
Class R4
C 000160037 [Member]
Class R6
Class R6
cik0000783740_SmallCapRisk2Member [Member]
Small Cap Risk
Small Cap Risk
cik0000783740_REITsRisk2Member [Member]
REITs Risk
REITs Risk
cik0000783740_Russell3000Index35Member [Member]
Russell 3000® Index
Russell 3000® Index
cik0000783740_Russell2000Index36Member [Member]
Russell 2000® Index
Russell 2000® Index
S 000054892 Summary4 [Member]
Prospectus Summary
Prospectus Summary
S 000054892 [Member]
MFS Blended Research Mid Cap Equity Fund
MFS Blended Research Mid Cap Equity Fund
C 000172715 [Member]
Class A
Class A
C 000172716 [Member]
Class B
Class B
C 000172717 [Member]
Class C
Class C
C 000172718 [Member]
Class I
Class I
C 000172719 [Member]
Class R1
Class R1
C 000172720 [Member]
Class R2
Class R2
C 000172721 [Member]
Class R3
Class R3
C 000172722 [Member]
Class R4
Class R4
C 000172723 [Member]
Class R6
Class R6
cik0000783740_MidCapRisk2Member [Member]
Mid Cap Risk
Mid Cap Risk
cik0000783740_Russell3000Index37Member [Member]
Russell 3000® Index
Russell 3000® Index
cik0000783740_RussellMidcapIndex38Member [Member]
Russell Midcap® Index
Russell Midcap® Index
S 000050660 Summary5 [Member]
Prospectus Summary
Prospectus Summary
S 000050660 [Member]
MFS Blended Research Value Equity Fund
MFS Blended Research Value Equity Fund
C 000160038 [Member]
Class A
Class A
C 000160039 [Member]
Class B
Class B
C 000160040 [Member]
Class C
Class C
C 000160041 [Member]
Class I
Class I
C 000160042 [Member]
Class R1
Class R1
C 000160043 [Member]
Class R2
Class R2
C 000160044 [Member]
Class R3
Class R3
C 000160045 [Member]
Class R4
Class R4
C 000160046 [Member]
Class R6
Class R6
cik0000783740_Russell3000Index39Member [Member]
Russell 3000® Index
Russell 3000® Index
cik0000783740_Russell1000ValueIndex310Member [Member]
Russell 1000® Value Index
Russell 1000® Value Index
S 000002510 Summary6 [Member]
Prospectus Summary
Prospectus Summary
S 000002510 [Member]
MFS Conservative Allocation Fund
MFS Conservative Allocation Fund
C 000006887 [Member]
Class A
Class A
C 000006892 [Member]
Class B
Class B
C 000006893 [Member]
Class C
Class C
C 000006894 [Member]
Class I
Class I
C 000006896 [Member]
Class R1
Class R1
C 000006898 [Member]
Class R2
Class R2
C 000006899 [Member]
Class R3
Class R3
C 000006888 [Member]
Class R4
Class R4
C 000231060 [Member]
Class R6
Class R6
cik0000783740_BloombergUSAggregateBondIndex311Member [Member]
Bloomberg U.S. Aggregate Bond Index
Bloomberg U.S. Aggregate Bond Index
cik0000783740_MFSConservativeAllocationFundBlendedIndex312Member [Member]
MFS Conservative Allocation Fund Blended Index
MFS Conservative Allocation Fund Blended Index
S 000002512 Summary7 [Member]
Prospectus Summary
Prospectus Summary
S 000002512 [Member]
MFS Emerging Markets Equity Fund
MFS Emerging Markets Equity Fund
C 000006904 [Member]
Class A
Class A
C 000006905 [Member]
Class B
Class B
C 000006906 [Member]
Class C
Class C
C 000006907 [Member]
Class I
Class I
C 000071424 [Member]
Class R1
Class R1
C 000071425 [Member]
Class R2
Class R2
C 000071426 [Member]
Class R3
Class R3
C 000071427 [Member]
Class R4
Class R4
C 000071428 [Member]
Class R6
Class R6
cik0000783740_MSCIEmergingMarketsIndexnetdiv313Member [Member]
MSCI Emerging Markets Index (net div)
MSCI Emerging Markets Index (net div)
S 000002514 Summary8 [Member]
Prospectus Summary
Prospectus Summary
S 000002514 [Member]
MFS Growth Allocation Fund
MFS Growth Allocation Fund
C 000006911 [Member]
Class A
Class A
C 000006916 [Member]
Class B
Class B
C 000006917 [Member]
Class C
Class C
C 000006918 [Member]
Class I
Class I
C 000006920 [Member]
Class R1
Class R1
C 000006922 [Member]
Class R2
Class R2
C 000006923 [Member]
Class R3
Class R3
C 000006912 [Member]
Class R4
Class R4
C 000231061 [Member]
Class R6
Class R6
cik0000783740_StandardPoors500StockIndex314Member [Member]
Standard & Poor's 500 Stock Index
Standard & Poor's 500 Stock Index
cik0000783740_MFSGrowthAllocationFundBlendedIndex315Member [Member]
MFS Growth Allocation Fund Blended Index
MFS Growth Allocation Fund Blended Index
S 000002515 Summary9 [Member]
Prospectus Summary
Prospectus Summary
S 000002515 [Member]
MFS International Diversification Fund
MFS International Diversification Fund
C 000006924 [Member]
Class A
Class A
C 000006929 [Member]
Class B
Class B
C 000006930 [Member]
Class C
Class C
C 000006931 [Member]
Class I
Class I
C 000006933 [Member]
Class R1
Class R1
C 000006935 [Member]
Class R2
Class R2
C 000006936 [Member]
Class R3
Class R3
C 000006925 [Member]
Class R4
Class R4
C 000195683 [Member]
Class R6
Class R6
cik0000783740_MSCIAllCountryWorldex-USIndexnetdiv316Member [Member]
MSCI All Country World (ex-US) Index (net div)
MSCI All Country World (ex-US) Index (net div)
S 000002516 Summary10 [Member]
Prospectus Summary
Prospectus Summary
S 000002516 [Member]
MFS International Growth Fund
MFS International Growth Fund
C 000006937 [Member]
Class A
Class A
C 000006938 [Member]
Class B
Class B
C 000006939 [Member]
Class C
Class C
C 000006940 [Member]
Class I
Class I
C 000071431 [Member]
Class R1
Class R1
C 000071432 [Member]
Class R2
Class R2
C 000071433 [Member]
Class R3
Class R3
C 000071430 [Member]
Class R4
Class R4
C 000034484 [Member]
Class R6
Class R6
cik0000783740_MSCIAllCountryWorldex-USIndexnetdiv317Member [Member]
MSCI All Country World (ex-US) Index (net div)
MSCI All Country World (ex-US) Index (net div)
cik0000783740_MSCIAllCountryWorldex-USGrowthIndexnetdiv318Member [Member]
MSCI All Country World (ex-US) Growth Index (net div)
MSCI All Country World (ex-US) Growth Index (net div)
S 000002517 Summary11 [Member]
Prospectus Summary
Prospectus Summary
S 000002517 [Member]
MFS International Intrinsic Equity Fund
MFS International Intrinsic Equity Fund
C 000006941 [Member]
Class A
Class A
C 000006942 [Member]
Class B
Class B
C 000006943 [Member]
Class C
Class C
C 000006944 [Member]
Class I
Class I
C 000071434 [Member]
Class R1
Class R1
C 000071435 [Member]
Class R2
Class R2
C 000071436 [Member]
Class R3
Class R3
C 000071437 [Member]
Class R4
Class R4
C 000034485 [Member]
Class R6
Class R6
cik0000783740_MSCIEAFEEuropeAustralasiaFarEastIndexnetdiv319Member [Member]
MSCI EAFE (Europe, Australasia, Far East) Index (net div)
MSCI EAFE (Europe, Australasia, Far East) Index (net div)
cik0000783740_MSCIEAFEEuropeAustralasiaFarEastValueIndexnetdiv320Member [Member]
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div)
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div)
S 000068882 Summary12 [Member]
Prospectus Summary
Prospectus Summary
S 000068882 [Member]
MFS International Value Fund
MFS International Value Fund
C 000220109 [Member]
Class A
Class A
C 000220112 [Member]
Class C
Class C
C 000220111 [Member]
Class I
Class I
C 000220110 [Member]
Class R1
Class R1
C 000220113 [Member]
Class R2
Class R2
C 000220108 [Member]
Class R3
Class R3
C 000220107 [Member]
Class R4
Class R4
C 000220106 [Member]
Class R6
Class R6
cik0000783740_MSCIEAFEEuropeAustralasiaFarEastIndexnetdiv321Member [Member]
MSCI EAFE (Europe, Australasia, Far East) Index (net div)
MSCI EAFE (Europe, Australasia, Far East) Index (net div)
cik0000783740_MSCIEAFEEuropeAustralasiaFarEastValueIndexnetdiv322Member [Member]
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div)
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div)
S 000045806 Summary13 [Member]
Prospectus Summary
Prospectus Summary
S 000045806 [Member]
MFS Managed Wealth Fund
MFS Managed Wealth Fund
C 000142775 [Member]
Class A
Class A
C 000142776 [Member]
Class B
Class B
C 000142777 [Member]
Class C
Class C
C 000142778 [Member]
Class I
Class I
C 000142779 [Member]
Class R1
Class R1
C 000142780 [Member]
Class R2
Class R2
C 000142781 [Member]
Class R3
Class R3
C 000142782 [Member]
Class R4
Class R4
C 000195688 [Member]
Class R6
Class R6
cik0000783740_StandardPoors500StockIndex323Member [Member]
Standard & Poor's 500 Stock Index
Standard & Poor's 500 Stock Index
cik0000783740_ICEBofA0-3MonthUSTreasuryBillIndex324Member [Member]
ICE BofA 0-3 Month U.S. Treasury Bill Index
ICE BofA 0-3 Month U.S. Treasury Bill Index
S 000002507 Summary14 [Member]
Prospectus Summary
Prospectus Summary
S 000002507 [Member]
MFS Moderate Allocation Fund
MFS Moderate Allocation Fund
C 000006851 [Member]
Class A
Class A
C 000006856 [Member]
Class B
Class B
C 000006857 [Member]
Class C
Class C
C 000006858 [Member]
Class I
Class I
C 000006860 [Member]
Class R1
Class R1
C 000006862 [Member]
Class R2
Class R2
C 000006863 [Member]
Class R3
Class R3
C 000006852 [Member]
Class R4
Class R4
C 000231059 [Member]
Class R6
Class R6
cik0000783740_StandardPoors500StockIndex325Member [Member]
Standard & Poor's 500 Stock Index
Standard & Poor's 500 Stock Index
cik0000783740_MFSModerateAllocationFundBlendedIndex326Member [Member]
MFS Moderate Allocation Fund Blended Index
MFS Moderate Allocation Fund Blended Index
Document [Axis]
Series [Axis]
Prospectus
Prospectus [Table]
Risk/Return:
Performance Measure [Axis]
Class [Axis]
Before Taxes
After Taxes on Distributions
After Taxes on Distributions and Sales
Risk [Axis]
All Risks [Member]
Risk Lose Money [Member]
Risk Not Insured [Member]
Risk Nondiversified Status [Member]
Risk Not Insured Depository Institution [Member]
Risk Money Market Fund Price Fluctuates [Member]
Risk Money Market Fund May Impose Fees or Suspend Sales [Member]
Risk Money Market Fund Sponsor May Not Provide Support [Member]
Risk Money Market Fund May Not Preserve Dollar [Member]
Risks [Table Text Block]
Risks [Table Text Block]