Changes in Fair Value of Capitalized MSRs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Servicing Assets at Fair Value [Line Items]
Balance at beginning of period	$ 1,594		$ 1,989		$ 1,519		$ 1,837
Rights purchased	10		5		39		16
Rights capitalized	224		101		700		416
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(123)	[1]	(534)	[1]	(298)	[1]	(569)	[1]
Due to revised assumptions or models	(2)	[2]	2	[2]	(19)	[2]	27	[2]
Other changes in fair value	(150)	[3]	(97)	[3]	(388)	[3]	(261)	[3]
Balance at end of period	$ 1,553		$ 1,466		$ 1,553		$ 1,466

[1] Includes changes in MSR value associated with changes in market interest rates, including estimated prepayment rates and anticipated earnings on escrow deposits.

[2] Includes changes in MSR value not caused by changes in market interest rates, such as changes in cost to service, ancillary income, and discount rate, as well as the impact of any model changes.

[3] Primarily represents changes due to realization of expected cash flows over time (decay).