Mortgage Loan Repurchase Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Reserve for mortgage loan repurchase losses
Balance at beginning of period	$ 434	$ 299	$ 320	$ 265
Repurchase provision	371	117	701	287
Charge-offs	(111)	(134)	(327)	(270)
Balance at end of period	$ 694	$ 282	$ 694	$ 282