Credit Quality (Summary of the Bancorp's Nonperforming Loans and Leases by Class) (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	$ 403,000,000	$ 437
OREO and other repossessed property	45,000,000	52
Nonperforming portfolio assets	448,000,000	489
Commercial Portfolio Segment
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	278,000,000	306,000,000
Commercial Portfolio Segment \| Commercial and Industrial Loans
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	240,000,000	276,000,000
Commercial Portfolio Segment \| Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	9,000,000	19,000,000
Commercial Portfolio Segment \| Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	3,000,000	7,000,000
Commercial Portfolio Segment \| Commercial Leases
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	26,000,000	4,000,000
Residential Mortgage Loans
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	23,000,000	30,000,000
Consumer Portfolio Segment
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	102,000,000	101,000,000
Consumer Portfolio Segment \| Home Equity
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	74,000,000	74,000,000
Consumer Portfolio Segment \| Automobile Loans
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	1,000,000	1,000,000
Consumer Portfolio Segment \| Credit Card
Financing Receivable, Modifications
Nonaccrual portfolio loans and leases	26,000,000	26,000,000
Consumer Portfolio Segment \| Other Consumer Loans
Financing Receivable, Modifications
Nonperforming portfolio assets	$ 1,000,000	$ 0

Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized and the carrying amount of other real estate and foreclosed assets, excluding government guaranteed loans.

No definition available.

+ Details

Name:	fitb_NonperformingPortfolioAssets
Namespace Prefix:	fitb_
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_FinancingReceivableModificationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

+ Details

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

- Definition

Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

+ 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(4))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=fitb_CommercialAndIndustrialLoansMember
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=fitb_CommercialLeasesMember
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_HomeEquityMember
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:

- Details

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