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Trading Assets and Liabilities and Derivatives - Additional Information (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral $ 935sti_AmountOfRepurchaseAgreementsSecuredByTradingAssets $ 1,100sti_AmountOfRepurchaseAgreementsSecuredByTradingAssets
Repurchase Agreements [Member]    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Trading Securities Pledged as Collateral 978us-gaap_TradingSecuritiesPledgedAsCollateral
/ us-gaap_InvestmentTypeAxis
= us-gaap_RepurchaseAgreementsMember		 1,100us-gaap_TradingSecuritiesPledgedAsCollateral
/ us-gaap_InvestmentTypeAxis
= us-gaap_RepurchaseAgreementsMember
Derivative [Member]    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Trading Securities Pledged as Collateral $ 234us-gaap_TradingSecuritiesPledgedAsCollateral
/ us-gaap_InvestmentTypeAxis
= us-gaap_DerivativeMember		 $ 202us-gaap_TradingSecuritiesPledgedAsCollateral
/ us-gaap_InvestmentTypeAxis
= us-gaap_DerivativeMember