Changes in the Servicing Asset Related to Residential Mortgage Loans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 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	305	236
Servicing Asset At Amortized Value Amortization	(186)	(135)
Carrying amount before valuation allowance	1,358	1,239
Valuation allowance for servicing assets:
Beginning balance	(558)	(316)
Servicing impairment	(103)	(242)
Ending balance	(661)	(558)
Carrying amount as of the end of the period	$ 697	$ 681