Capital One Financial Corporation (Parent Company Only) - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities:
Net income	$ 920	$ 1,114	$ 863	$ 1,153	$ 999	$ 1,081	$ 1,194	$ 1,154	$ 4,050	$ 4,428	$ 4,121
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Net cash provided by operating activities									10,127	9,304	9,984
Investing activities:
Purchase of securities available for sale									(12,200)	(12,650)	(14,951)
Net cash (used) provided by investing activities									(29,726)	(15,991)	3,721
Common Stock
Net proceeds from issuances									111	100	81
Dividends paid—common stock									(816)	(679)	(555)
Preferred Stock
Net proceeds from issuances									1,472	969	0
Dividends paid—preferred stock									(158)	(67)	(53)
Purchases of treasury stock									(2,441)	(2,045)	(1,033)
Proceeds from stock-based payment activities									85	146	114
Net cash provided (used) by financing activities									20,380	7,638	(18,472)
Increase (decrease) in cash and cash equivalents									781	951	(4,767)
Cash and cash equivalents at beginning of the period				7,242				6,291	7,242	6,291	11,058
Cash and cash equivalents at end of the period	8,023				7,242				8,023	7,242	6,291
Parent Company
Operating activities:
Net income									4,050	4,428	4,121
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Equity in undistributed Net Income including Discontinued Ops									(3,766)	(1,112)	1,576
Other Operating Activities, Cash Flow Statement									(300)	(83)	(1,120)
Net cash provided by operating activities									(16)	3,233	4,577
Investing activities:
Decrease (increase) in investment in subsidiaries									(172)	94	787
Proceeds from maturities of securities available for sale									65	50	46
Purchase of securities available for sale									0	(143)	(287)
Increase (Decrease) in Loans to Subsidiaries									973	(7)	(153)
Net cash (used) provided by investing activities									866	(6)	393
Financing activities:
Increase (decrease) in borrowings from subsidiaries									18	28	(3,490)
Issuance of senior notes									2,487	1,498	849
Maturities of senior notes									(2,625)	(2,100)	(1,040)
Common Stock
Net proceeds from issuances									111	100	81
Dividends paid—common stock									(816)	(679)	(555)
Preferred Stock
Net proceeds from issuances									1,472	969	0
Dividends paid—preferred stock									(158)	(67)	(53)
Purchases of treasury stock									(2,441)	(2,045)	(1,033)
Proceeds from stock-based payment activities									85	146	114
Net cash provided (used) by financing activities									(1,867)	(2,150)	(5,127)
Increase (decrease) in cash and cash equivalents									(1,017)	1,077	(157)
Cash and cash equivalents at beginning of the period				$ 8,262				$ 7,185	8,262	7,185	7,342
Cash and cash equivalents at end of the period	$ 7,245				$ 8,262				$ 7,245	$ 8,262	$ 7,185