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Loans and Leases - Schedule of Allowance for Loan Losses (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans and Leases Evaluated for Impairment $ 18,319us-gaap_LoansAndLeasesReceivableGrossCarryingAmount $ 18,199us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Institutional    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans and Leases Evaluated for Impairment 18,284us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stt_InstitutionalMember		 18,171us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stt_InstitutionalMember
Amount of loan losses related to institutional loans collectively evaluated for impairment 41us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stt_InstitutionalMember		 38us-gaap_FinancingReceivableCollectivelyEvaluatedForImpairment
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stt_InstitutionalMember
Commercial Real Estate    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans and Leases Evaluated for Impairment 35us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 28us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Collectively Evaluated for Impairment    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans and Leases Evaluated for Impairment 18,319us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= stt_CollectivelyEvaluatedforImpairmentMember		 18,199us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_InternalCreditAssessmentAxis
= stt_CollectivelyEvaluatedforImpairmentMember
Collectively Evaluated for Impairment | Institutional    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans and Leases Evaluated for Impairment 18,284us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stt_InstitutionalMember
/ us-gaap_InternalCreditAssessmentAxis
= stt_CollectivelyEvaluatedforImpairmentMember		 18,171us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= stt_InstitutionalMember
/ us-gaap_InternalCreditAssessmentAxis
= stt_CollectivelyEvaluatedforImpairmentMember
Collectively Evaluated for Impairment | Commercial Real Estate    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans and Leases Evaluated for Impairment $ 35us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_InternalCreditAssessmentAxis
= stt_CollectivelyEvaluatedforImpairmentMember		 $ 28us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_InternalCreditAssessmentAxis
= stt_CollectivelyEvaluatedforImpairmentMember