Net Securities Gains (Losses) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Gain (Loss) on Investments [Line Items]
Realized gross gains	$ 122	$ 62	$ 67	$ 184	$ 86
Realized gross losses	(5)		(11)	(5)	(20)
Recognized gross impairments	(67)	(22)	(8)	(89)	(13)
Net securities gains (losses)	$ 50	$ 40	$ 48	$ 90	$ 53