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Goodwill and Other Intangible Assets - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Goodwill and Intangible Assets Disclosure [Abstract] |  |  |  |
Amortization of intangibles | $ 20 | $ 24 | $ 58 | $ 60

X
- Definition Amortization and impairment of Intangibles + References No definition available. + Details
Name: | cof_AmortizationAndImpairmentOfIntangibles
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_GoodwillAndIntangibleAssetsDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration