Regulatory and Capital Adequacy - Capital Ratios Under Basel III (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2022 USD ($)
Common equity Tier 1 capital:
Common equity Tier 1 capital	$ 43,501	$ 44,731
Common equity Tier 1 capital, capital ratio	0.131	0.125
Common equity Tier 1 capital, minimum capital adequacy	0.045	0.045
Tier 1 risk-based capital:
Tier 1 capital	$ 48,346	$ 49,576
Tier 1 capital, capital ratio	0.145	0.139
Tier 1 capital, minimum capital adequacy	0.060	0.060
Tier 1 capital, well-capitalized	0.060	0.060
Total risk-based capital:
Total capital	$ 56,089	$ 56,714
Total capital, capital ratio	0.169	0.158
Total capital, minimum capital adequacy	0.080	0.080
Total capital, well-capitalized	0.100	0.100
Tier 1 leverage capital:
Tier 1 leverage capital	$ 48,346	$ 49,576
Tier 1 leverage, capital ratio	0.116	0.111
Tier 1 leverage, minimum capital adequacy	0.040	0.040
Supplementary leverage:
Tier one capital under BaselIII standardized approach	$ 48,346	$ 49,576
Basel III Supplementary Leverage Ratio	0.099	0.095
Supplementary leverage	0.030	0.030
Regulatory Capital Adjustments, Net of Tax, CECL Transition	$ 2,400
Common Equity Tier One Capital Ratio, Excluding CECL Transition Adjustment		12.00%
Common Equity Tier One Capital Ratio, CECL Transition		12.50%
Capital One, N.A.
Common equity Tier 1 capital:
Common equity Tier 1 capital	$ 26,699	$ 46,630
Common equity Tier 1 capital, capital ratio	0.111	0.131
Common equity Tier 1 capital, minimum capital adequacy	0.045	0.045
Common equity Tie 1 capital, well capitalized	0.065	0.065
Tier 1 risk-based capital:
Tier 1 capital	$ 26,699	$ 46,630
Tier 1 capital, capital ratio	0.111	0.131
Tier 1 capital, minimum capital adequacy	0.060	0.060
Tier 1 capital, well-capitalized	0.080	0.080
Total risk-based capital:
Total capital	$ 29,449	$ 51,165
Total capital, capital ratio	0.122	0.144
Total capital, minimum capital adequacy	0.080	0.080
Total capital, well-capitalized	0.100	0.100
Tier 1 leverage capital:
Tier 1 leverage capital	$ 26,699	$ 46,630
Tier 1 leverage, capital ratio	0.074	0.105
Tier 1 leverage, minimum capital adequacy	0.040	0.040
Tier 1 leverage, well-capitalized	0.050	0.050
Supplementary leverage:
Tier one capital under BaselIII standardized approach	$ 26,699	$ 46,630
Basel III Supplementary Leverage Ratio	0.066	0.090
Supplementary leverage	0.030	0.030