Mortgage Loan Repurchase Losses (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reserve for mortgage loan repurchase losses
Balance at beginning of period	$ 320	$ 265	$ 200
Repurchase provision	713	502	456
Charge-offs	(401)	(447)	(391)
Balance at end of period	$ 632	$ 320	$ 265