Litigation Settlement, Amount Attributable to Reporting Entity and Third Party

No definition available.

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

- Definition

Number of consumer class action cases filed for Cybersecurity Incident

+ References

No definition available.

+ Details

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Namespace Prefix:	cof_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14435-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118942415&loc=d3e14557-108349

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118943654&loc=d3e12021-110248

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_LitigationCaseAxis=cof_AntiMoneyLaunderingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LitigationStatusAxis=us-gaap_PendingLitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=cof_InterchangeLitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_CA
Namespace Prefix:
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Commitments, Contingencies, Guarantees, and Others - Litigation (Detail) $ in Millions		1 Months Ended
	Dec. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Mar. 31, 2020 USD ($) claim
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss \| $			$ 1,200
Number of consumer class action cases filed for Cybersecurity Incident \| claim			73
Anti-money laundering
Loss Contingencies [Line Items]
Litigation settlement paid \| $		$ 100
Pending litigation \| Interchange litigation
Loss Contingencies [Line Items]
Litigation settlement, attributable to reporting entity and third party \| $	$ 5,500
United States
Loss Contingencies [Line Items]
Number of consumer class action cases filed for Cybersecurity Incident \| claim			61
Canada
Loss Contingencies [Line Items]
Number of consumer class action cases filed for Cybersecurity Incident \| claim			12