Capital One Financial Corporation (Parent Company Only) - Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income	$ 1,982	$ 3,751	$ 4,050
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Net cash from operating activities	14,182	11,856	10,127
Investing activities:
Purchase of securities available for sale	(12,412)	(14,154)	(12,200)
Net cash from investing activities	(15,541)	(25,630)	(29,726)
Common Stock
Net proceeds from issuances	164	131	111
Dividends paid	(780)	(812)	(816)
Preferred Stock
Net proceeds from issuances	0	1,066	1,472
Dividends paid	(265)	(214)	(158)
Purchases of treasury stock	(240)	(3,661)	(2,441)
Proceeds from share-based payment activities	124	142	85
Net cash from financing activities	3,218	17,227	21,163
Cash, cash equivalents and restricted cash for securitization investors, beginning of the period	9,976
Cash, cash equivalents and restricted cash for securitization investors, ending of the period	14,040	9,976
Parent Company
Operating activities:
Net income	1,982	3,751	4,050
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Equity in undistributed earnings of subsidiaries	(1,797)	65	(3,766)
Other operating activities	327	(10)	(300)
Net cash from operating activities	512	3,806	(16)
Investing activities:
Net payments (to) from subsidiaries	(4,956)	(163)	(172)
Proceeds from paydowns and maturities of securities available for sale	130	71	65
Changes in loans to subsidiaries	44	(71)	973
Net cash from investing activities	(4,782)	(163)	866
Financing activities:
Changes in borrowings from subsidiaries	23	19	18
Proceeds from issuance of senior notes and sub notes	6,948	1,487	2,487
Proceeds from paydowns and maturities of senior and subordinated notes	(804)	(1,750)	(2,625)
Common Stock
Net proceeds from issuances	164	131	111
Dividends paid	(780)	(812)	(816)
Preferred Stock
Net proceeds from issuances	0	1,066	1,472
Dividends paid	(265)	(214)	(158)
Purchases of treasury stock	(240)	(3,661)	(2,441)
Proceeds from share-based payment activities	124	142	85
Net cash from financing activities	5,170	(3,592)	(1,867)
Changes in cash and cash equivalents	900	51	(1,017)
Cash, cash equivalents and restricted cash for securitization investors, beginning of the period	7,296	7,245	8,262
Cash, cash equivalents and restricted cash for securitization investors, ending of the period	$ 8,196	$ 7,296	$ 7,245