Credit Quality and the Allowance for Loan and Lease Losses - Summary of Loans Modified in a TDR (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1,237	1,802	4,577	4,982
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 129	$ 121	$ 422	$ 279
(Decrease) Increase to ALLL Upon Modification	(5)	2	26	(8)
Charge-offs Recognized Upon Modification	$ 8	$ 1	$ 8	$ 8
Commercial \| Commercial and industrial loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	33	27	96	65
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 75	$ 72	$ 250	$ 168
(Decrease) Increase to ALLL Upon Modification	1	(1)	25	(15)
Charge-offs Recognized Upon Modification	$ 7	$ 0	$ 7	$ 5
Commercial \| Commercial mortgage owner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	10	4	38	13
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 19	$ 1	$ 38	$ 10
(Decrease) Increase to ALLL Upon Modification	(3)	0	(3)	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Commercial \| Commercial mortgage nonowner-occupied loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	3		15
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 16		$ 38
(Decrease) Increase to ALLL Upon Modification	(2)		(2)
Charge-offs Recognized Upon Modification	$ 0		$ 0
Commercial \| Commercial construction loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan			3
Amortized Cost Basis of Loans Modified in a TDR During the Period			$ 21
(Decrease) Increase to ALLL Upon Modification			1
Charge-offs Recognized Upon Modification			$ 0
Residential Mortgage
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	66	256	359	531
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 11	$ 39	$ 48	$ 74
(Decrease) Increase to ALLL Upon Modification	0	1	1	1
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer \| Home equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	88	21	130	58
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 2	$ 1	$ 6	$ 3
(Decrease) Increase to ALLL Upon Modification	(3)	0	(4)	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer \| Indirect secured consumer loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	14	27	56	65
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 0	$ 0	$ 0	$ 0
(Decrease) Increase to ALLL Upon Modification	0	0	0	0
Charge-offs Recognized Upon Modification	$ 0	$ 0	$ 0	$ 0
Consumer \| Credit card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period \| loan	1,023	1,467	3,880	4,250
Amortized Cost Basis of Loans Modified in a TDR During the Period	$ 6	$ 8	$ 21	$ 24
(Decrease) Increase to ALLL Upon Modification	2	2	8	6
Charge-offs Recognized Upon Modification	$ 1	$ 1	$ 1	$ 3

Amount of credit loss expense (reversal of expense) for financing receivable from change in methodology.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 11
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919244-210447

+ Details

Name:	us-gaap_FinancingReceivableChangeInMethodCreditLossExpenseReversal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18845-111554

+ Details

Name:	us-gaap_FinancingReceivablesImpairedTroubledDebtRestructuringWriteDown
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fitb_CommercialMortgageLoansOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fitb_CommercialMortgageLoansNonOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_AutomobileLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CreditCardReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: