Adjusted Carrying Values for Assets Measured at Fair Value on Nonrecurring Basis (Detail) (Fair Value, Measurements, Nonrecurring, USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 138	[1]	$ 168	[1]
Other assets	204	[2]	310	[2]
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans		[1]
Other assets		[2]
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans		[1]
Other assets		[2]
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	138	[1]	168	[1]
Other assets	$ 204	[2]	$ 310	[2]

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

[2] Primarily represents the fair value of foreclosed properties that were measured at fair value based on an appraisal or broker price opinion of the collateral subsequent to their initial acquisition.