Capital One Financial Corporation (Parent Company Only) - Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Interest from temporary investments	$ 27,176	$ 25,222	$ 22,891
Interest expense	4,301	2,762	2,018
Non-interest income	5,201	4,777	4,628
Non-interest expense	14,902	14,194	13,558
Income tax (benefit)	1,293	3,375	1,714
Net income	6,015	1,982	3,751
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	5,879	2,005	3,418
Parent Company
Condensed Income Statements, Captions [Line Items]
Interest from temporary investments	313	178	120
Interest expense	720	381	258
Dividends from Subsidiaries	2,750	300	3,936
Non-interest income	19	19	(13)
Non-interest expense	29	34	48
Income before income taxes and equity in undistributed earnings of subsidiaries	2,333	82	3,737
Income tax (benefit)	(128)	(103)	(79)
Income (loss) from subsidiary including discontinued operations, net of tax	3,554	1,797	(65)
Net income	6,015	1,982	3,751
Other Comprehensive Income (Loss), Net of Tax	(136)	23	(333)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 5,879	$ 2,005	$ 3,418