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v3.25.4

Securities - Additional Information (Details) $ in Billions | Dec. 31, 2025 USD ($)
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Investments, Debt and Equity Securities [Abstract] |
Securities pledged to secure securities sold under repurchase agreements | $ 18.7

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- Definition Debt Securities, Available For Sale And Held To Maturity, Pledged + References No definition available. + Details
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Namespace Prefix: | key_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration