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Commitments, Contingencies, Guarantees, and Others - Loss Sharing and UK PPI (Details) - USD ($) $ in Millions | Sep. 30, 2022 | Dec. 31, 2021
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Loss sharing agreements |  |
Loss Contingencies [Line Items] |  |
Guarantee obligation | $ 85 | $ 90

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- Definition The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248 + Details
Name: | us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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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
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_GuaranteeObligationsByNatureAxis=cof_LossSharingAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |