Fair Value Measurements (Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Residential Mortgage Loans Measured at Fair Value) (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Residential mortgage loans
Aggregate fair value
Loans measured at fair value	$ 1,750	$ 1,447
Past due loans of 90 days or more	2	2
Non accrual loans	1	1
Aggregate unpaid principal balance
Loans measured at fair value	1,659	1,410
Past due loans of 90 days or more	2	2
Non accrual loans	1	1
Difference
Loans measured at fair value	91	37
Past due loans of 90 days or more	0	0
Non accrual loans	0	$ 0
Commercial loans
Aggregate fair value
Loans measured at fair value	8
Aggregate unpaid principal balance
Loans measured at fair value	9
Difference
Loans measured at fair value	$ (1)

Fair value option loans held as assets 90 days or more past due aggregate unpaid principal.

No definition available.

Name:	fitb_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDueAggregateUnpaidPrincipal
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value option loans held as assets aggregate unpaid principal balance abstract.

+ References

No definition available.

+ Details

Name:	fitb_FairValueOptionLoansHeldAsAssetsAggregateUnpaidPrincipalBalanceAbstractAbstract
Namespace Prefix:	fitb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value option loans held as assets amount in non accrual status aggregate unpaid principal.

+ References

No definition available.

+ Details

Name:	fitb_FairValueOptionLoansHeldAsAssetsAmountInNonAccrualStatusAggregateUnpaidPrincipal
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion loans receivable disclosure.

+ References

No definition available.

+ Details

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

- Definition

Mortgages held for sale unpaid principal.

+ References

No definition available.

+ Details

Name:	fitb_MortgagesHeldForSaleUnpaidPrincipal
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are 90 days or more past due.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

Name:	us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDueAggregateDifference
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

This item represents the aggregate fair value of loans held as assets that are in nonaccrual status for which the fair value option has been elected, if the entity's policy is to recognize interest income separately from other changes in fair value.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(2)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

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

- Definition

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

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

- Definition

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

+ Details

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

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: