Allowance for Credit Losses and Reserve for Unfunded Lending Commitments - Charge-Offs (Details) $ in Millions	3 Months Ended
Mar. 31, 2023 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
2023	$ 3
2022	166
2021	175
2020	88
2019	67
Prior	38
Total Term Loans	537
Revolving Loans	1,684
Revolving Loans Converted to Term	21
Total	2,242
Credit Card
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	1,666
Revolving Loans Converted to Term	21
Total	1,687
Credit Card \| Domestic Card
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	1,569
Revolving Loans Converted to Term	18
Total	1,587
Credit Card \| International card businesses
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving Loans	97
Revolving Loans Converted to Term	3
Total	100
Consumer Banking
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1
2022	160
2021	175
2020	88
2019	53
Prior	38
Total Term Loans	515
Revolving Loans	16
Revolving Loans Converted to Term	0
Total	531
Consumer Banking \| Auto
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1
2022	160
2021	175
2020	88
2019	53
Prior	38
Total Term Loans	515
Revolving Loans	0
Revolving Loans Converted to Term	0
Total	515
Consumer Banking \| Retail banking
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0
2022	0
2021	0
2020	0
2019	0
Prior	0
Total Term Loans	0
Revolving Loans	16
Revolving Loans Converted to Term	0
Total	16
Commercial Banking
Financing Receivable, Credit Quality Indicator [Line Items]
2023	2
2022	6
2021	0
2020	0
2019	14
Prior	0
Total Term Loans	22
Revolving Loans	2
Revolving Loans Converted to Term	0
Total	24
Commercial Banking \| Commercial and multifamily real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0
2022	4
2021	0
2020	0
2019	14
Prior	0
Total Term Loans	18
Revolving Loans	0
Revolving Loans Converted to Term	0
Total	18
Commercial Banking \| Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2023	2
2022	2
2021	0
2020	0
2019	0
Prior	0
Total Term Loans	4
Revolving Loans	2
Revolving Loans Converted to Term	0
Total	$ 6

Financing Receivable, Excluding Accrued Interest, Originated, More than Five Years before Current Fiscal Year, Writeoff

No definition available.

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Period Type:	duration

- Definition

Financing Receivable, Excluding Accrued Interest, Revolving, Converted to Term Loan, Writeoff

+ References

No definition available.

+ Details

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- Definition

Financing Receivable, Excluding Accrued Interest, Revolving, Writeoff

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

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- Definition

Financing Receivable, Excluding Accrued Interest, Year Five, Originated, Four Years before Current Fiscal Year, Writeoff

+ References

No definition available.

+ Details

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- Definition

Financing Receivable, Excluding Accrued Interest, Year Four, Originated, Three Years before Current Fiscal Year, Writeoff

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Financing Receivable, Excluding Accrued Interest, Year One, Originated, Current Fiscal Year, Writeoff

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Financing Receivable, Excluding Accrued Interest, Year Three, Originated, Two Years before Current Fiscal Year, Writeoff

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Financing Receivable, Excluding Accrued Interest, Year Two, Originated, Fiscal Year before Current Fiscal Year, Writeoff

+ References

No definition available.

+ Details

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Namespace Prefix:	cof_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

+ Details

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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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