Mortgage Loan Repurchase Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Reserve for mortgage loan repurchase losses
Balance at beginning of period	$ 632	$ 320
Repurchase provision	14	175
Charge-offs	(133)	(112)
Balance at end of period	$ 513	$ 383