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v3.21.1

Business Segment Reporting - Additional Information (Details) | Mar. 31, 2021 sector branch
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Consumer Bank |
Segment Reporting Information [Line Items] |
Number of state branch networks | branch | 15
Commercial Bank |
Segment Reporting Information [Line Items] |
Number of industry sectors | sector | 7

X
- Definition Number of industrial sectors. + References No definition available. + Details
Name: | key_NumberOfIndustrialSectors
Namespace Prefix: | key_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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: |

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