Credit Quality (Credit Quality Additional Information) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Troubled Debt Restructuring
Line of credit commitments for modified troubled debt restructurings	$ 53	$ 78
Letter of credit commitments for modified troubled debt restructurings	82	57
Mortgage loans in process of foreclosure amount	235	260
Commercial aggregate borrower relationship subject to individual review for impairment	$ 1	$ 1

Commercial aggregate borrower relationship subject to individual review for impairment

No definition available.

Name:	fitb_CommercialAggregateBorrowerRelationship
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	fitb_LetterOfCreditCommitments
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	fitb_LineOfCreditCommitments
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL49126937-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

+ Details

Name:	us-gaap_MortgageLoansInProcessOfForeclosureAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_TroubledDebtRestructuringDebtorCurrentPeriodAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration