Commitments, Contingencies and Guarantees - Additional Information (Detail) (Standby and commercial letters of credit [Member], USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Standby and commercial letters of credit [Member]
Line of credit, current	$ 6,045
Term of standby and commercial letters of credit commitments	One year or less
Period of minimum rate of return on investment term	Twelve-year weighted average period
Investor capital and minimum investment yield	168
Unamortized fair value of guarantee fee	7
Current exposure to loss	37
Future exposure to loss	$ 42