XML 51 R52.htm IDEA: XBRL DOCUMENT v2.4.1.9
Asset Quality - Nonperforming Assets and Past Due Loans (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]      
Purchased credit impaired loans $ 12key_PurchasedCreditImpairedLoansOutstandingPrincipalBalance $ 13key_PurchasedCreditImpairedLoansOutstandingPrincipalBalance $ 16key_PurchasedCreditImpairedLoansOutstandingPrincipalBalance
Restructured loans 18us-gaap_TroubledDebtRestructuringDebtorSubsequentPeriodsContingentPaymentsAmount 17us-gaap_TroubledDebtRestructuringDebtorSubsequentPeriodsContingentPaymentsAmount 15us-gaap_TroubledDebtRestructuringDebtorSubsequentPeriodsContingentPaymentsAmount
Residential Mortgage [Member]      
Financing Receivable, Recorded Investment, Past Due [Line Items]      
Carrying value of foreclosed residential real estate 119us-gaap_MortgageLoansOnRealEstateForeclosures
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember		    
Residential Real Estate [Member]      
Financing Receivable, Recorded Investment, Past Due [Line Items]      
Carrying value of foreclosed residential real estate $ 17us-gaap_MortgageLoansOnRealEstateForeclosures
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialRealEstateMember