Losses Recognized Related to Nonrecurring Fair Value Measurements of Individual Assets or Portfolios (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
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 12	[1]	$ 32	[1]	$ 51	[1]	$ 153	[1]
Other assets	$ 42	[2]	$ 81	[2]	$ 129	[2]	$ 230	[2]

[1] Represents write-downs of loans which were based on the fair value of the collateral, excluding loans fully charged-off.

[2] Primarily represents related losses of foreclosed properties that were measured at fair value subsequent to their initial acquisition.