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Securities Available for Sale - Additional Information (Detail) (USD $)
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale Securities Pledged as Collateral $ 3,100,000,000us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral $ 2,600,000,000us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral  
Available-for-sale Securities 26,761,000,000us-gaap_AvailableForSaleSecurities [1] 26,770,000,000us-gaap_AvailableForSaleSecurities [1]  
Mortgage-backed Securities, Issued by Private Enterprises [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale Securities 119,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember		 123,000,000us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember		  
Other Than Temporarily Impaired Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale Securities $ 0us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= sti_OtherThanTemporarilyImpairedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember		   $ 0us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= sti_OtherThanTemporarilyImpairedSecuritiesMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $0 million and $369 million at March 31, 2015 and December 31, 2014, respectively.