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Derivative Financial Instruments - Narrative (Details) (USD $)
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Derivative [Line Items]      
Cash collateral received for derivative instruments $ 1,490,000,000stt_CashCollateralReceivedForDerivativeInstruments   $ 1,790,000,000stt_CashCollateralReceivedForDerivativeInstruments
Cash collateral provided for derivative instruments 4,870,000,000stt_CashCollateralProvidedForDerivativeInstruments   4,790,000,000stt_CashCollateralProvidedForDerivativeInstruments
Fair value of derivative liabilities 17,397,000,000us-gaap_DerivativeFairValueOfDerivativeLiability   15,234,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
Maximum additional amount of payments related to termination events 0us-gaap_AdditionalCollateralAggregateFairValue    
Securities weighted average life (in years) 5 years 8 months 15 days 5 years 10 months 18 days  
OCI, change in gain (loss) of fair value hedge, net of tax 15,000,000stt_OtherComprehensiveIncomeLossChangeInUnrealizedGainLossOnAfsSecuritiesDesignatedAsFairValueHedgesNetOfRelatedTaxes 10,000,000stt_OtherComprehensiveIncomeLossChangeInUnrealizedGainLossOnAfsSecuritiesDesignatedAsFairValueHedgesNetOfRelatedTaxes  
Fair Value Hedges | 1.35% Senior Note      
Derivative [Line Items]      
Fixed interest rate 1.35%us-gaap_DerivativeFixedInterestRate
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_InvestmentTypeAxis
= stt_OnePointThreeFiveSeniorNoteMember		    
Fair Value Hedges | 3.70% notes due in 2023      
Derivative [Line Items]      
Fixed interest rate 3.70%us-gaap_DerivativeFixedInterestRate
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_InvestmentTypeAxis
= stt_ThreePointSevenZeroPercentSeniorNotesDue2023Member		    
Fair Value Hedges | 3.30% notes due 2024      
Derivative [Line Items]      
Fixed interest rate 3.30%us-gaap_DerivativeFixedInterestRate
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_InvestmentTypeAxis
= stt_ThreePointThreeZeroPercentNotesDue2024Member		    
Credit swap agreements      
Derivative [Line Items]      
Fair value of derivative liabilities 2,160,000,000us-gaap_DerivativeFairValueOfDerivativeLiability
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditDefaultSwapMember		    
Maximum additional amount of payments related to termination events $ 2,000,000,000us-gaap_AdditionalCollateralAggregateFairValue
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_CreditDefaultSwapMember		    
Interest rate swap | Fair Value Hedges | 3.1% Subordinated Note      
Derivative [Line Items]      
Fixed interest rate 3.10%us-gaap_DerivativeFixedInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember
/ us-gaap_InvestmentTypeAxis
= stt_ThreePoineOneSubordinatedNoteMember		    
Interest rate swap | Fair Value Hedges | Senior notes      
Derivative [Line Items]      
Number of securities 3us-gaap_DerivativeNumberOfInstrumentsHeld
/ us-gaap_DebtInstrumentAxis
= us-gaap_SeniorNotesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember		    
Interest rate swap | Fair Value Hedges | Subordinated note      
Derivative [Line Items]      
Number of securities 1us-gaap_DerivativeNumberOfInstrumentsHeld
/ us-gaap_DebtInstrumentAxis
= us-gaap_SubordinatedDebtMember
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= us-gaap_FairValueHedgingMember