Investment Securities - Changes in Credit Losses on Debt Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investments Debt And Equity Securities [Abstract]
Balance at beginning of period	$ 133	$ 288	$ 134	$ 298
Credit losses on securities not previously considered other-than-temporarily impaired		2		3
Decreases in expected cash flows on securities for which other-than-temporary impairment was previously recognized	3	11	10	19
Total other-than-temporary impairment on debt securities	3	13	10	22
Increases in expected cash flows	(1)	(8)	(1)	(14)
Realized losses (a)	(6)	(16)	(14)	(29)
Credit losses on security sales and securities expected to be sold	(5)		(5)
Balance at end of period	$ 124	$ 277	$ 124	$ 277