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Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract] |  |  |
Uncollectible portion of billed finance charges and fees | $ 2,600 | $ 1,900 | $ 946

X
- Definition Uncollectible Portion of Billed Finance Charges and Fees + References No definition available. + Details
Name: | cof_UncollectiblePortionofBilledFinanceChargesandFees
Namespace Prefix: | cof_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_AccountsNotesLoansAndFinancingReceivableGrossAllowanceAndNetAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration