Accumulated Other Comprehensive Income - Change in AOCI Gain (Loss) by Component (Net of Tax) (Parenthetical) (Detail) (USD $) In Billions, unless otherwise specified	Sep. 30, 2013
Equity [Abstract]
Held to maturity securities fair value	$ 18.3
Net pre-tax unrealized losses	$ 1.5

Available-for-sale Securities, Transfers to Held-to-maturity, Unrealized losses

No definition available.

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