Changes in the Servicing Asset Related to Residential Mortgage Loans (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 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	190	105
Amortization	(86)	(53)
Carrying amount before valuation allowance	1,343	1,190
Valuation allowance for servicing assets:
Beginning balance	(558)	(316)
Servicing impairment	(49)	(27)
Ending balance	(607)	(343)
Carrying amount as of the end of the period	$ 736	$ 847