Changes in the Servicing Asset Related to Residential Mortgage Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Servicing Assets at Fair Value [Line Items]
Carrying amount as of the beginning of the period	$ 1,239	$ 1,138
Servicing obligations that result from the transfer of residential mortgage loans	121	63
Amortization	(46)	(28)
Carrying amount before valuation allowance	1,314	1,173
Valuation allowance for servicing assets:
Beginning balance	(558)	(316)
Servicing impairment	11	37
Ending balance	(547)	(279)
Carrying amount as of the end of the period	$ 767	$ 894