Risk Ratings of the Notional Amount of Risk Participation Agreements (Detail) (Interest Rate Contract, Lender Concentration Risk, USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Notional amount of the risk participation agreements	$ 723	$ 851	$ 824
Pass
Notional amount of the risk participation agreements	645	744	520
Risk Level, Substandard
Notional amount of the risk participation agreements	43	69	11
Risk Level, Doubtful
Notional amount of the risk participation agreements		1	8
Risk Level, Special Mention
Notional amount of the risk participation agreements	34	37	225
Unlikely to be Collected Financing Receivable
Notional amount of the risk participation agreements	$ 1		$ 60