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Summary of Significant Accounting and Reporting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Significant Accounting Policies [Line Items]  
Established threshold nonaccrual commercial loans $ 1fitb_CommercialLoansOnNonaccrualStatus
Established threshold impaired loans on accrual status 1fitb_ImpairedLoansAccrualStatus
Larger commercial loans, subject to impairment review 1fitb_LoansAndLeasesReceivableImpairedCarryingValue
Established threshold commercial loans not subject to specific allowance calculations $ 1fitb_CreditRiskRelatedContingentFeaturesCollateralThreshold