Loans - Composition of Loans Held-for-Investment Portfolio (Parenthetical) (Detail) (USD $) In Billions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Construction loans and land development loans	$ 2.2	$ 2.1

Reflects the gross carrying amount of unpaid loans that had been issued to businesses to construct a facility and/or develop land for sale or construction thereon. Acquisition, development and construction (ADC) loans are generally issued sequentially and the net proceeds of the latest debt is used by the borrower to pay off the preceding loan. A construction loan is generally expected to be paid off with the net proceeds from permanent financing.

No definition available.

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