Derivatives and Hedging Activities - Fair Value of Credit Derivatives Purchased and Sold (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Credit Derivatives [Line Items]
Purchased	$ (2)	$ (3)
Sold	(1)	0
Net	(3)	(3)
Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Purchased	(1)	(1)
Sold	0	0
Net	(1)	(1)
Traded Credit Default Swap Indices [Member]
Credit Derivatives [Line Items]
Purchased	(1)	(2)
Sold	0	0
Net	(1)	(2)
Other [Member]
Credit Derivatives [Line Items]
Purchased	0	0
Sold	(1)	0
Net	$ (1)	$ 0