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Fair Value - Level 3 Total Realized And Unrealized Gains And Losses Recorded In Revenue (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Total Revenue [Member]    
Realized and Unrealized Gains and Losses [Line Items]    
Total Realized and Unrealized Gains (Losses) Recorded in Revenue $ 35stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TotalRevenueMember		 $ 17stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TotalRevenueMember
Change in Unrealized Gains (Losses) Related to Financial Instruments Held 14stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TotalRevenueMember		 (2)stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TotalRevenueMember
Trading services    
Realized and Unrealized Gains and Losses [Line Items]    
Total Realized and Unrealized Gains (Losses) Recorded in Revenue 22stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TradingServicesMember		 (1)stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TradingServicesMember
Change in Unrealized Gains (Losses) Related to Financial Instruments Held 14stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TradingServicesMember		 (2)stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TradingServicesMember
Total fee revenue    
Realized and Unrealized Gains and Losses [Line Items]    
Total Realized and Unrealized Gains (Losses) Recorded in Revenue 22stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TotalFeeRevenueMember		 (1)stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TotalFeeRevenueMember
Change in Unrealized Gains (Losses) Related to Financial Instruments Held 14stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TotalFeeRevenueMember		 (2)stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= stt_TotalFeeRevenueMember
Net interest revenue    
Realized and Unrealized Gains and Losses [Line Items]    
Total Realized and Unrealized Gains (Losses) Recorded in Revenue 13stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_InterestIncomeMember		 18stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_InterestIncomeMember
Change in Unrealized Gains (Losses) Related to Financial Instruments Held $ 0stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_InterestIncomeMember		 $ 0stt_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLossIncludedInTradingRevenue
/ us-gaap_IncomeStatementLocationAxis
= us-gaap_InterestIncomeMember