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Fair Value Measurements - Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Residential Mortgage Loans Measured at Fair Value (Details) - Residential mortgage loans - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Aggregate Fair Value
Residential mortgage loans measured at fair value	$ 672	$ 682
Past due loans of 30-89 days	2	1
Past due loans of 90 days or more	1	1
Nonaccrual loans	3	2
Aggregate Unpaid Principal Balance
Residential mortgage loans measured at fair value	668	693
Past due loans of 30-89 days	2	1
Past due loans of 90 days or more	1	1
Nonaccrual loans	$ 3	$ 2

X

- Definition

Fair Value, Option, Loans Held as Assets, 30-89 Days Past Due

+ References

No definition available.

+ Details

Name:	fitb_FairValueOptionLoansHeldAsAssets3089DaysPastDue
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

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

+ References

No definition available.

+ Details

Name:	fitb_FairValueOptionLoansHeldAsAssets3089DaysPastDueAggregateUnpaidPrincipal
Namespace Prefix:	fitb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

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

+ References

No definition available.

+ Details

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

X

- 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

X

- 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

X

- 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

X

- Definition

Mortgage Loans, Aggregate Unpaid Principal

+ References

No definition available.

+ Details

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

X

- 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://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (e)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-28

+ Details

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

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- References

No definition available.

+ Details

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

X

- 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://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (e)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-28

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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