Capital One Financial Corporation (Parent Company Only) - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets:
Cash and cash equivalents	$ 21,746	$ 40,509
Other assets	22,816	21,205
Total assets	432,381	421,602
Liabilities:
Senior and subordinated notes	27,219	27,382
Other liabilities	17,005	15,065
Total liabilities	371,352	361,398
Stockholders’ equity:
Stockholders' Equity Attributable to Parent	61,029	60,204	$ 58,011	$ 51,668
Total liabilities and stockholders’ equity	432,381	421,602
Parent Company
Assets:
Cash and cash equivalents	16,910	12,976
Investments in subsidiaries	57,600	62,066
Receivables From Subsidiaries	7,849	5,924
Securities available for sale (amortized cost of $94.9 billion and $97.6 billion and allowance for credit losses of $1 million as of both December 31, 2021 and 2020)	513	622
Other assets	1,330	1,473
Total assets	84,202	83,061
Liabilities:
Senior and subordinated notes	23,017	22,037
Other liabilities	156	820
Total liabilities	23,173	22,857
Stockholders’ equity:
Stockholders' Equity Attributable to Parent	61,029	60,204
Total liabilities and stockholders’ equity	$ 84,202	$ 83,061