Risk Ratings of the Notional Amount of Risk Participation Agreements (Detail) (Interest Rate Contract, Lender Concentration Risk, USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010
Notional amount of the risk participation agreements	$ 722	$ 851	$ 776
Pass
Notional amount of the risk participation agreements	654	744	516
Risk Level, Substandard
Notional amount of the risk participation agreements	54	69	11
Risk Level, Doubtful
Notional amount of the risk participation agreements	4	1	7
Risk Level, Special Mention
Notional amount of the risk participation agreements	9	37	192
Unlikely to be Collected Financing Receivable
Notional amount of the risk participation agreements	$ 1		$ 50