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Business Segment Reporting - Additional Information (Details)	Dec. 31, 2023 state
Consumer Bank
Segment Reporting Information [Line Items]
Number of state branch network	15

X

- Definition

Number of state branch network.

+ References

No definition available.

+ Details

Name:	key_NumberOfStateBranchNetwork
Namespace Prefix:	key_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

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

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=key_ConsumerBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: