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Payment Status for the LHFI Portfolio (Additional Information) (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Financing Receivable, Impaired [Line Items]    
Loans Receivable, Fair Value Disclosure $ 268us-gaap_LoansReceivableFairValueDisclosure $ 272us-gaap_LoansReceivableFairValueDisclosure
Nonaccruing 90 Plus Days Past Due 379sti_FinancingReceivableRecordedInvestment90DaysPastDueNonaccrualStatus 388sti_FinancingReceivableRecordedInvestment90DaysPastDueNonaccrualStatus
Residential Portfolio Segment [Member]    
Financing Receivable, Impaired [Line Items]    
Loans Receivable, Fair Value Disclosure $ 268us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember		 $ 272us-gaap_LoansReceivableFairValueDisclosure
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ResidentialPortfolioSegmentMember