Income Taxes (Reconciliation of the Beginning and Ending Amounts of the Bancorp's Unrecognized Tax Benefits) (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Unrecognized Tax Benefits Exceptional Adjustments	$ 6	$ 5

Unrecognized tax benefits exceptional adjustments.

No definition available.

Name:	fitb_UnrecognizedTaxBenefitsExceptionalAdjustments
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration