Guarantee Arrangements and Pledged Assets - Net Credit Derivative Positions (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Carrying (Fair) Value [Member]
Credit Derivatives [Line Items]
Sell-protection credit derivative positions	$ 621		$ 76
Buy-protection credit derivative positions	777		120
Net position	156	[1]	44	[1]
Notional [Member]
Credit Derivatives [Line Items]
Sell-protection credit derivative positions	229,166		237,548
Buy-protection credit derivative positions	234,311		247,384
Net position	$ 5,145	[1]	$ 9,836	[1]

[1] Positions are presented net in the table above to provide a complete analysis of our risk exposure and depict the way we manage our credit derivative portfolio. The offset of the sell-protection credit derivatives against the buy-protection credit derivatives may not be legally binding in the absence of master netting agreements with the same counterparty. Furthermore, the credit loss triggering events for individual sell protection credit derivatives may not be the same or occur in the same period as those of the buy protection credit derivatives thereby not providing an exact offset.