Investment Securities - Schedule of Contractual Maturities for Available for Sale Securities (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Amortized Cost
Due in 1 year or less	$ 646
Due after 1 year through 5 years	3,112
Due after 5 years through 10 years	6,602
Due after 10 years	30,851
Total Amortized Cost	41,211	$ 40,733
Fair Value
Due in 1 year or less	647
Due after 1 year through 5 years	3,132
Due after 5 years through 10 years	6,589
Due after 10 years	30,892
Available-for-sale Securities	$ 41,260	$ 40,737