Changes in the Servicing Asset Related to Residential Mortgage Loans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Servicing Assets at Fair Value [Line Items]
Carrying amount as of the beginning of the period	$ 1,138	$ 979
Servicing obligations that result from the transfer of residential mortgage loans	236	297
Amortization	(135)	(138)
Carrying amount before valuation allowance	1,239	1,138
Valuation allowance for servicing assets:
Beginning balance	(316)	(280)
Servicing impairment	(242)	(36)
Ending balance	(558)	(316)
Carrying amount as of the end of the period	$ 681	$ 822