Commitments, Contingencies and Guarantees - Additional Information (Detail) (Standby and commercial letters of credit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Standby and commercial letters of credit [Member]
Concentration Risk [Line Items]
Term of standby and commercial letters of credit commitments	One year or less
Standby and commercial letters of credit, current	$ 5,930
Period of minimum rate of return on investment term	Twelve-year weighted average period
Investor capital and minimum investment yield	162
Unamortized fair value of guarantee fee	6
Current exposure to loss	31
Future exposure to loss	$ 39