Activity Related to the MSR Portfolio (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Servicing Assets at Fair Value [Line Items]
Gain Loss On Sale Of Securities Net Economic Hedge Servicing Rights	$ 3	$ 9	$ 14
Changes Fair Value Of Free Standing Derivatives	63	344	109
Mortgage Servicing Rights (MSR) Impairment (Recovery)	$ (103)	$ (242)	$ (36)