Assets Measured at Fair Value on Nonrecurring Basis (Detail) (Fair Value, Measurements, Nonrecurring, USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 257	[1]	$ 221	[1]
Other assets	111	[2]	126	[2]
Total assets	368		347
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	213	[1]	178	[1]
Other assets	111	[2]	126	[2]
Total assets	324		304
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	44	[1]	43	[1]
Total assets	$ 44		$ 43

[1] During the quarters ended March 31, 2012 and Dec. 31, 2011, the fair value of these loans was reduced $13 million and $32 million, respectively, based on the fair value of the underlying collateral as allowed by ASC 310, Accounting by Creditors for Impairment of a Loan, with an offset to the allowance for credit losses.

[2] Includes other assets received in satisfaction of debt and loans held for sale. Loans held for sale are carried on the balance sheet at the lower of cost or market value.