Investment Securities - Changes in Credit Losses on Debt Securities Excluding Perpetual Preferred Securities (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Credit Losses on Debt Securities [RollForward]
Balance at beginning of period	$ 96	$ 111	$ 101	$ 116
Decreases in expected cash flows on securities for which other-than-temporary impairment was previously recognized		3		3
Total other-than-temporary impairment on debt securities		3		3
Increases in expected cash flows			(2)	(2)
Realized losses	(5)	(3)	(8)	(6)
Credit losses on security sales and securities expected to be sold	0	0	0	0
Balance at end of period	$ 91	$ 111	$ 91	$ 111