Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2012	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Outstanding principal balances at period end of residential mortgage loans serviced for others	$ 18,121			$ 18,930
Outstanding principal balances at period end of residential mortgage loans owned and serviced for others	36,773			$ 37,544
Purchased from HSBC Finance account of credit card			$ 746
Credit card receivables not being sold to Capital One at a fair value			108
Fair value of Intangible asset related to account relationships purchased include in branch sale			43
Fair value of Intangible asset related to account relationships purchased retained			$ 65
Residential mortgage banking revenue [Member]
Finite-Lived Intangible Assets [Line Items]
Servicing fees collected	$ 13	$ 15
Purchased credit card relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Useful life			10 years