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v3.19.3.a.u2

Summary of Significant Accounting Policies - Customer Rewards Reserve and Revenue Recognition (Details) - USD ($) $ in Billions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items] |  |
Customer Reward Program | $ 4.7 | $ 4.3
Minimum |  |
Loans and Leases Receivable Disclosure [Line Items] |  |
Partnership Agreement Initial Term | 2 years |
Maximum |  |
Loans and Leases Receivable Disclosure [Line Items] |  |
Partnership Agreement Initial Term | 10 years |
Credit Card |  |
Loans and Leases Receivable Disclosure [Line Items] |  |
Loan Commitment and Origination Fees and Discounts or Premiums, Amortization Period | 12 months |
Amortization term of annual membership fees | 12 months |

X
- Definition Amortization term of credit card annual membership fees + References No definition available. + Details
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Namespace Prefix: | cof_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Carrying amount as of the balance sheet date of liability related to rewards benefits earned by card holders. + References No definition available. + Details
Name: | cof_CustomerLoyaltyProgramLiability
Namespace Prefix: | cof_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Loan Commitment and Origination Fees and Discounts or Premiums, Amortization Period + References No definition available. + Details
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Namespace Prefix: | cof_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Partnership Agreement Initial Term + References No definition available. + Details
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Namespace Prefix: | cof_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablePortfolioSegmentAxis=cof_CreditCardPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |