Adjustment to portfolio asset lower of cost or fair value.

No definition available.

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

- Definition

Finance charge and fees reserves.

+ References

No definition available.

+ Details

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

- Definition

Loans and Leases Receivable, Minimum Individual Loan Balance Requiring Annual Review

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

Loans and Leases Receivable, Minimum Individual Loan Balance Requiring Quarterly Review

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Loans and Leases Receivable, Number of Portfolio Segments

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans subject to the sale agreement and transferred to loans held for sale.

+ References

No definition available.

+ Details

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

- Definition

Loans Sold, Percent Retained Servicing

+ References

No definition available.

+ Details

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Namespace Prefix:	cof_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Uncollectible Portion of Billed Finance Charges and Fees

+ References

No definition available.

+ Details

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

- Details

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

- Definition

The balance of financing receivables that were acquired with deteriorated credit quality.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524

+ Details

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

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

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Balance Type:	debit
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- Definition

Amount classified as loans attributable to disposal group held for sale or disposed of. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph a

-Article 9

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(a))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 35

-Paragraph 49

-URI http://asc.fasb.org/extlink&oid=35742846&loc=d3e3084-111518

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 310

-Section 30

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6490209&loc=d3e48214-111002

+ Details

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

- Definition

The amount of cash paid for the origination of mortgages that are held for sale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

+ Details

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

- Definition

Unused amount of commitments to extend credit to customers.

+ References

No definition available.

+ Details

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

- Details

Name:	cof_FinancingReceivablePortfolioSegmentAxis=cof_CreditCardPortfolioSegmentMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

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- Details

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- Details

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- Details

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- Details

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Loans - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended	12 Months Ended
Loans - Additional Information (Detail) (USD $)	Sep. 06, 2013	Mar. 31, 2013	Dec. 31, 2014 Segment	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of portfolio segments			3
Acquired loans accounted for based on expected cash flows			$ 23,500,000,000	$ 28,550,000,000
Assets subject to sale agreement, loan		7,000,000,000
Adjustment to portfolio asset lower of cost or fair value	26,000,000
Loans held for sale			626,000,000us-gaap_LoansReceivableHeldForSaleNet	218,000,000us-gaap_LoansReceivableHeldForSaleNet
Troubled debt restructurings included in impaired loans			1,700,000,000	1,700,000,000
Finance charge and fees reserve			216,000,000cof_FinanceChargeAndFeesReserves	190,000,000cof_FinanceChargeAndFeesReserves
Revenue
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reduction in revenue, uncollectible portion of billed finance charges and fees			645,000,000	796,000,000	937,000,000
Consumer Banking \| Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings included in impaired loans			1,000,000,000	1,100,000,000
Commercial Banking \| Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings included in impaired loans			194,000,000	180,000,000
Residential Mortgage Loans And Commercial Multifamily Real Estate Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Origination of conforming residential mortgage loans and commercial multifamily real estate loans			5,400,000,000	2,100,000,000	1,600,000,000
Percentage of servicing on conforming residential mortgage loans and commercial multifamily real estate loans retained after sale			96.00%	92.00%	92.00%
Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans accounted for based on expected cash flows			192,000,000	262,000,000
Commercial Banking \| Criticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum loan amount reviewed quarterly by management for further deterioration			1,000,000
Commercial Banking \| Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum loan amount requiring annual review			1,000,000
Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Acquired loans accounted for based on expected cash flows			23,000,000	63,000,000
Unused credit card lines available to customers			292,900,000,000	276,700,000,000
Other Portfolio Segments, Excluding Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unused credit card lines available to customers			$ 23,600,000,000	$ 20,900,000,000