Investment Securities - Schedule of Contractual Maturities of Securities Held to Maturity (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Carrying Value
Due after 1 year through 5 years	$ 199
Due after 5 years through 10 years	1,150
Due after 10 years	22,362
Carrying Value	23,711	$ 22,500
Fair Value
Due after 1 year through 5 years	200
Due after 5 years through 10 years	1,244
Due after 10 years	23,469
Fair Value	$ 24,913	$ 23,634