Guarantee Arrangements and Pledged Assets - Net Credit Derivative Positions (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Carrying (Fair) Value [Member]
Credit Derivatives [Line Items]
Sell-protection credit derivative positions	$ (1,194)	$ (7,759)
Buy-protection credit derivative positions	1,162	8,131
Net position	(32)	372
Notional [Member]
Credit Derivatives [Line Items]
Sell-protection credit derivative positions	262,985	330,395
Buy-protection credit derivative positions	263,055	326,882
Net position	$ (70)	$ 3,513