Capital One Financial Corporation (Parent Company Only) - Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, Captions [Line Items]
Interest from temporary investments	$ 25,222	$ 22,891	$ 20,459
Interest expense	2,762	2,018	1,625
Non-interest income	4,777	4,628	4,579
Non-interest expense	14,194	13,558	12,996
Income tax (benefit)	3,375	1,714	1,869
Net income	1,982	3,751	4,050
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	2,005	3,418	3,864
Parent Company
Condensed Income Statements, Captions [Line Items]
Interest from temporary investments	178	120	120
Interest expense	381	258	185
Dividends from Subsidiaries	300	3,936	450
Non-interest income	19	(13)	10
Non-interest expense	34	48	178
Income before income taxes and equity in undistributed earnings of subsidiaries	82	3,737	217
Income tax (benefit)	(103)	(79)	(67)
Income (loss) from subsidiary including discontinued operations, net of tax	1,797	(65)	3,766
Net income	1,982	3,751	4,050
Other Comprehensive Income (Loss), Net of Tax	23	(333)	(186)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 2,005	$ 3,418	$ 3,864