Investment Securities - Changes in Credit Losses on Debt Securities Excluding Perpetual Preferred Securities (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Credit Losses on Debt Securities [RollForward]
Balance at beginning of period	$ 91	$ 111	$ 101	$ 116
Decreases in expected cash flows on securities for which other-than-temporary impairment was previously recognized				3
Total other-than-temporary impairment on debt securities				3
Increases in expected cash flows		(2)	(2)	(4)
Realized losses	(3)	(4)	(11)	(10)
Balance at end of period	$ 88	$ 105	$ 88	$ 105