Derivatives and Hedging Activities - Fair Value of Credit Derivatives Purchased and Sold (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Credit Derivatives [Line Items]
Purchased	$ (3)	$ 10	$ 17
Sold	4	(8)	(14)
Net	1	2	3
Single Name Credit Default Swaps
Credit Derivatives [Line Items]
Purchased	(2)	3	9
Sold		(1)	(5)
Net	(2)	2	4
Traded Credit Default Swap Indices
Credit Derivatives [Line Items]
Purchased	(1)	6	6
Sold	5	(6)	(8)
Net	4		(2)
Other
Credit Derivatives [Line Items]
Purchased		1	2
Sold	(1)	(1)	(1)
Net	$ (1)		$ 1