Troubled Debt Restructuring Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Troubled Debt Restructuring [Line Items]
Line of credit commitments for modified troubled debt restructurings	$ 21	$ 27	$ 42
Letter of credit commitments for modified troubled debt restructurings	$ 26	$ 4	$ 1

Letter of credit commitments to lend additional funds to debtors owing receivables whose terms have been modified in a troubled debt restructuring.

No definition available.

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