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v3.25.4

Business Segment Reporting - Additional Information (Details) | Dec. 31, 2025 state
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Consumer Bank |
Segment Reporting Information [Line Items] |
Number of state branch footprint | 15
Commercial Bank |
Segment Reporting Information [Line Items] |
Number of state branch footprint | 15

X
- Definition The number of states the entity operates in as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix: | us-gaap_
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: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=key_CommercialBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |