Carryover basis of shares.

No definition available.

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

- Definition

Letters Credit Issued Related Variable Rate Demand Notes.

+ References

No definition available.

+ Details

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

- Definition

Outstanding repurchase demand inventory.

+ References

No definition available.

+ Details

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

- Definition

Percentage Of Letter Of Credit.

+ References

No definition available.

+ Details

Name:	fitb_PercentageOfLetterOfCredit
Namespace Prefix:	fitb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Repurchase demand request.

+ References

No definition available.

+ Details

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

- Definition

Repurchased Outstanding Principal.

+ References

No definition available.

+ Details

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

- Definition

Reserve For Unfunded Credit Commitments.

+ References

No definition available.

+ Details

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

- Definition

Stock Received In Initial Public Offering Shares.

+ References

No definition available.

+ Details

Name:	fitb_StockReceivedInInitialPublicOfferingShares
Namespace Prefix:	fitb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Variable Rate Demand Notes.

+ References

No definition available.

+ Details

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

- Definition

Carrying value as of the balance sheet date of the sum of the obligations to contract holders to provide to them an agreed upon rate of return pursuant to the terms of the underlying contract. These contracts represent lending by the contract holders to the entity in return for a guaranteed (primarily fixed) interest rate until maturity, unless called earlier if the contracts provide that option to the contract holders (usually institutions). There is little or no insurance risk for the entity.

+ References

+ Details

Name:	us-gaap_BorrowingsUnderGuaranteedInvestmentAgreements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

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

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14557-108349

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121555522&loc=d3e12021-110248

+ Details

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

- Definition

The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8,17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_NotesPayable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of valuation and qualifying accounts and reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09(Column B))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24092-122690

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09(Column E))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24092-122690

+ Details

Name:	us-gaap_ValuationAllowancesAndReservesBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_CreditCardIntermediaryReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=us-gaap_VariableRateDemandObligationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InformationByCategoryOfDebtSecurityAxis=us-gaap_TradingAssetsExcludingDebtAndEquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments, Contingent Liabilities and Guarantees - Additional Information (Details) - USD ($) shares in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Sep. 30, 2019	Jun. 30, 2018	Sep. 30, 2014	Sep. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2008
Loss Contingencies
Margin account balance held by the brokerage clearing agent	$ 24,000,000		$ 14,000,000
Visa
Loss Contingencies
Fair value of liability	195,000,000		201,000,000
Visa IPO, shares of Visa's Class B common stock received												10.1
Visa Class B shares carryover basis												$ 0
Escrow deposit				$ 300,000,000	$ 600,000,000	$ 450,000,000	$ 150,000,000	$ 1,565,000,000	$ 400,000,000	$ 800,000,000	$ 500,000,000	$ 3,000,000,000
Residential mortgage loans
Loss Contingencies
Fair value of liability	8,000,000
Repurchased outstanding principal	10,000,000	$ 6,000,000
Repurchase demand request	10,000,000	$ 10,000,000
Outstanding repurchase demand inventory	4,000,000		5,000,000
Secured Debt
Loss Contingencies
Fully and unconditionally guaranteed certain long-term borrowing obligations issued by wholly-owned issuing trust entities	62,000,000		62,000,000
Standby Letters of Credit
Loss Contingencies
Reserve for unfunded commitments	$ 26,000,000		$ 27,000,000
Standby letters of credit as a percentage of total letters of credit	99.00%		99.00%
Standby Letters of Credit \| Secured Debt
Loss Contingencies
Standby letters of credit as a percentage of total letters of credit	70.00%		68.00%
Variable Rate Demand Note
Loss Contingencies
Total variable rate demand notes	$ 383,000,000		$ 385,000,000
Fifth Third Securities, Inc. (FTS) acted as the remarketing agent to issuers of VRDNs	383,000,000		385,000,000
Letters of credit issued related to variable rate demand notes	140,000,000		142,000,000
Variable Rate Demand Note \| Trading Securities
Loss Contingencies
Total variable rate demand notes	0		0
Other Liabilities
Loss Contingencies
Reserve for unfunded commitments	173,000,000		172,000,000
Other Liabilities \| Residential mortgage loans
Loss Contingencies
Outstanding balances on residential mortgage loans sold with representation and warranty provisions	$ 8,000,000		$ 8,000,000