Investment Securities - Schedule of Contractual Maturities for Available for Sale Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost
Due in 1 year or less	$ 1,025
Due after 1 year through 5 years	4,100
Due after 5 years through 10 years	3,382
Due after 10 years	32,226
Total Amortized Cost	40,733	$ 38,804
Fair Value
Due in 1 year or less	1,027
Due after 1 year through 5 years	4,106
Due after 5 years through 10 years	3,350
Due after 10 years	32,254
Available-for-sale Securities	$ 40,737	$ 39,061