Regulatory and Capital Adequacy - Schedule of Comparison of Capital Ratios (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Common equity Tier 1 capital:
Common equity Tier 1 capital	$ 29,534cof_CommonEquityTierOneCapital
Common equity Tier 1 capital, capital ratio	12.46%
Common equity Tier 1 capital, minimum capital adequacy	4.00%
Tier 1 common capital:
Tier 1 common capital		27,375cof_TierOneCommonCapital
Tier 1 common capital ratio		12.19%cof_TierOneCommonCapitalRatio
Tier 1 risk-based capital:
Tier 1 risk-based capital	31,355us-gaap_TierOneRiskBasedCapital	28,230us-gaap_TierOneRiskBasedCapital
Tier 1 risk-based capital, capital ratio	13.23%	12.57%
Tier 1 risk-based capital, minimum capital adequacy	5.50%	4.00%
Tier 1 risk-based capital, well-capitalized	6.00%	6.00%
Total risk-based capital:
Total risk-based capital	35,879us-gaap_Capital	32,987us-gaap_Capital
Total risk-based capital, capital ratio	15.14%us-gaap_CapitalToRiskWeightedAssets	14.69%us-gaap_CapitalToRiskWeightedAssets
Total risk-based capital, minimum capital adequacy	8.00%	8.00%
Total risk-based capital, well-capitalized	10.00%	10.00%
Tier 1 leverage capital:
Tier 1 leverage capital	31,355us-gaap_TierOneLeverageCapital	28,230us-gaap_TierOneLeverageCapital
Tier 1 leverage, capital ratio	10.77%	10.06%
Tier 1 leverage, minimum capital adequacy	4.00%	4.00%
Capital One Bank (USA), N.A.
Common equity Tier 1 capital:
Common equity Tier 1 capital	8,503
Common equity Tier 1 capital, capital ratio	11.33%
Common equity Tier 1 capital, minimum capital adequacy	4.00%
Tier 1 risk-based capital:
Tier 1 risk-based capital	8,503	8,103
Tier 1 risk-based capital, capital ratio	11.33%	11.47%
Tier 1 risk-based capital, minimum capital adequacy	5.50%	4.00%
Tier 1 risk-based capital, well-capitalized	6.00%	6.00%
Total risk-based capital:
Total risk-based capital	10,938	10,528
Total risk-based capital, capital ratio	14.57%	14.90%
Total risk-based capital, minimum capital adequacy	8.00%	8.00%
Total risk-based capital, well-capitalized	10.00%	10.00%
Tier 1 leverage capital:
Tier 1 leverage capital	8,503	8,103
Tier 1 leverage, capital ratio	9.64%	10.21%
Tier 1 leverage, minimum capital adequacy	4.00%	4.00%
Tier 1 leverage, well-capitalized	5.00%	5.00%
Capital One, N.A.
Common equity Tier 1 capital:
Common equity Tier 1 capital	21,136
Common equity Tier 1 capital, capital ratio	12.53%
Common equity Tier 1 capital, minimum capital adequacy	4.00%
Tier 1 risk-based capital:
Tier 1 risk-based capital	21,136	19,930
Tier 1 risk-based capital, capital ratio	12.53%	12.67%
Tier 1 risk-based capital, minimum capital adequacy	5.50%	4.00%
Tier 1 risk-based capital, well-capitalized	6.00%	6.00%
Total risk-based capital:
Total risk-based capital	22,881	21,645
Total risk-based capital, capital ratio	13.57%	13.76%
Total risk-based capital, minimum capital adequacy	8.00%	8.00%
Total risk-based capital, well-capitalized	10.00%	10.00%
Tier 1 leverage capital:
Tier 1 leverage capital	$ 21,136	$ 19,930
Tier 1 leverage, capital ratio	8.90%	8.96%
Tier 1 leverage, minimum capital adequacy	4.00%	4.00%
Tier 1 leverage, well-capitalized	5.00%	5.00%

Common equity Tier 1 capital under BASEL III

No definition available.

Name:	cof_CommonEquityTierOneCapital
Namespace Prefix:	cof_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Common equity Tier 1 capital ratio is a regulatory capital measure under Basel III calculated based on common equity Tier 1 capital divided by risk-weighted assets.

+ References

No definition available.

+ Details

Name:	cof_CommonEquityTierOneCapitaltoRiskWeightedAssets
Namespace Prefix:	cof_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	cof_Tier1commoncapitalAbstract
Namespace Prefix:	cof_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Tier One common capital under Basel I

+ References

No definition available.

+ Details

Name:	cof_TierOneCommonCapital
Namespace Prefix:	cof_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Tier 1 common capital ratio is a regulatory capital measure under Basel I calculated based on Tier 1 common capital divided by Basel I risk-weighted asset.

+ References

No definition available.

+ Details

Name:	cof_TierOneCommonCapitalRatio
Namespace Prefix:	cof_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier One Common Capital Required for Capital Adequacy to Risk Weighted Assets

+ References

No definition available.

+ Details

Name:	cof_TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets
Namespace Prefix:	cof_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	cof_TierOneCommonEquityAbstract
Namespace Prefix:	cof_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of total capital as defined in the regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

+ Details

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

- Details

Name:	us-gaap_CapitalAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1H

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_RiskBasedRatiosAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

+ References

+ Details

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

- Details

Name:	us-gaap_TierOneLeverageCapitalAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Leverage Capital divided by average assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TierOneLeverageCapitalToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Risk Based Capital as defined in the regulations.

+ References

+ Details

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

- Definition

The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=cof_CapitalOneBankUSAN.A.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=cof_CapitalOneN.A.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: