Derivatives and Hedging Activities - Fair Value of Credit Derivatives Purchased and Sold (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Credit Derivatives [Line Items]
Purchased	$ (5)	$ (1)	$ (7)
Sold			8
Credit derivatives, net	(5)	(1)	1
Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Purchased	(4)	(1)	(6)
Sold		1	4
Credit derivatives, net	(4)		(2)
Traded Credit Default Swap Indices [Member]
Credit Derivatives [Line Items]
Purchased	(1)		(1)
Sold			5
Credit derivatives, net	(1)		4
Other [Member]
Credit Derivatives [Line Items]
Purchased
Sold		(1)	(1)
Credit derivatives, net		$ (1)	$ (1)