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Fair Value Measurement - Nonrecurring Fair Value Measurements Included in Earnings (Details) - Nonrecurring - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2021 | Mar. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Loans held for investment | $ (16) | $ (207)
Other assets | (36) | (44)
Total | $ (52) | $ (251)

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- Definition Gain (Loss) On Fair Value Assets measured on nonrecurring basis + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Gain (Loss) On Fair Value Loans Held For Investment measured on nonrecurring basis + References No definition available. + Details
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Namespace Prefix: | cof_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Gain (Loss) On Fair Value Other Assets measured on nonrecurring basis + References No definition available. + Details
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Namespace Prefix: | cof_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- 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
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- Details
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