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Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Residential Mortgage Loans Measured at Fair Value (Detail) (Residential mortgage loans, USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Residential mortgage loans
    
Aggregate fair value    
Residential mortgage loans measured at fair value $ 669fitb_FairValuePortionLoansReceivableDisclosure
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember		 $ 982fitb_FairValuePortionLoansReceivableDisclosure
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember
Past due loans of 90 days or more 2us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember		 1us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember
Nonaccrual loans 3us-gaap_FairValueOptionLoansHeldAsAssetsAggregateAmountInNonaccrualStatus
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember		 2us-gaap_FairValueOptionLoansHeldAsAssetsAggregateAmountInNonaccrualStatus
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember
Aggregate unpaid principal balance    
Residential mortgage loans measured at fair value 643fitb_MortgagesHeldForSaleUnpaidPrincipal
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember		 962fitb_MortgagesHeldForSaleUnpaidPrincipal
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember
Past due loans of 90 days or more 2fitb_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDueAggregateUnpaidPrincipal
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember		 2fitb_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDueAggregateUnpaidPrincipal
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember
Nonaccrual loans 3fitb_FairValueOptionLoansHeldAsAssetsAmountInNonaccrualStatusAggregateUnpaidPrincipal
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember		 2fitb_FairValueOptionLoansHeldAsAssetsAmountInNonaccrualStatusAggregateUnpaidPrincipal
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember
Difference    
Residential mortgage loans measured at fair value 26us-gaap_FairValueOptionLoansHeldAsAssetsAggregateDifference
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember		 20us-gaap_FairValueOptionLoansHeldAsAssetsAggregateDifference
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember
Past due loans of 90 days or more   $ (1)us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDueAggregateDifference
/ us-gaap_FinancialInstrumentAxis
= us-gaap_ResidentialMortgageMember