Investment Securities - Changes in Credit Losses on Debt Securities (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Credit Losses on Debt Securities [RollForward]
Balance at beginning of period	$ 81	$ 96	$ 84	$ 101
Decreases in expected cash flows on securities for which other-than-temporary impairment was previously recognized	1		1
Total other-than-temporary impairment on debt securities	1		1
Increases in expected cash flows	(1)		(1)	(2)
Realized losses	(2)	(5)	(5)	(8)
Balance at end of period	$ 79	$ 91	$ 79	$ 91