Investment Securities - Changes in Credit Losses on Debt Securities Excluding Perpetual Preferred Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Credit Losses on Debt Securities [RollForward]
Balance at beginning of period	$ 101	$ 116
Increases in expected cash flows	(2)	(2)
Realized losses	(3)	(3)
Balance at end of period	$ 96	$ 111