Variable Interest Entities and Securitizations - Carrying Amount of Assets and Liabilities of Variable Interest Entities (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Carrying Amount of Assets, Consolidated	$ 33,671	$ 35,152
Carrying Amount of Liabilities, Consolidated	15,726	17,026
Carrying Amount of Assets, Unconsolidated	4,192	4,120
Carrying Amount of Liabilities, Unconsolidated	554	582
Maximum exposure to loss	4,854	4,782
Affordable housing entities
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Total Assets	11,300	11,400
Carrying Amount of Assets, Consolidated	115	0
Carrying Amount of Liabilities, Consolidated	0	0
Carrying Amount of Assets, Unconsolidated	3,804	3,852
Carrying Amount of Liabilities, Unconsolidated	528	555
Maximum exposure to loss	3,804	3,852
Entities that provide capital to low-income and rural communities
Variable Interest Entity [Line Items]
Carrying Amount of Assets, Consolidated	687	352
Carrying Amount of Liabilities, Consolidated	126	101
Carrying Amount of Assets, Unconsolidated	71	0
Carrying Amount of Liabilities, Unconsolidated	0	0
Maximum exposure to loss	71	0
Other
Variable Interest Entity [Line Items]
Carrying Amount of Assets, Consolidated	0	0
Carrying Amount of Liabilities, Consolidated	0	0
Carrying Amount of Assets, Unconsolidated	116	57
Carrying Amount of Liabilities, Unconsolidated	0	0
Maximum exposure to loss	116	57
Total Other VIEs
Variable Interest Entity [Line Items]
Carrying Amount of Assets, Consolidated	802	352
Carrying Amount of Liabilities, Consolidated	126	101
Carrying Amount of Assets, Unconsolidated	3,991	3,909
Carrying Amount of Liabilities, Unconsolidated	528	555
Maximum exposure to loss	3,991	3,909
Credit card loan securitizations
Variable Interest Entity [Line Items]
Carrying Amount of Assets, Consolidated	32,869	34,800
Carrying Amount of Liabilities, Consolidated	15,600	16,925
Carrying Amount of Assets, Unconsolidated	0	0
Carrying Amount of Liabilities, Unconsolidated	0	0
Maximum exposure to loss	0	0
Home loan
Variable Interest Entity [Line Items]
Carrying Amount of Assets, Consolidated	0	0
Carrying Amount of Liabilities, Consolidated	0	0
Carrying Amount of Assets, Unconsolidated	201	211
Carrying Amount of Liabilities, Unconsolidated	26	27
Maximum exposure to loss	863	873
Total securitization-related VIEs
Variable Interest Entity [Line Items]
Carrying Amount of Assets, Consolidated	32,869	34,800
Carrying Amount of Liabilities, Consolidated	15,600	16,925
Carrying Amount of Assets, Unconsolidated	201	211
Carrying Amount of Liabilities, Unconsolidated	26	27
Maximum exposure to loss	$ 863	$ 873

Variable Interest Entity, Nonconsolidated, Total Assets

No definition available.

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

- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5710-111685

+ Details

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

- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

+ Details

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

- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5747-111685

+ Details

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Balance Type:	credit
Period Type:	instant

- 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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Period Type:	duration

- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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Period Type:	instant

- Definition

Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

+ References

+ Details

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