Securities Financing Activities - Summarized Securities Financing Agreements (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Collateral [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements		$ (2)	$ (2)
Total offsetting of financial assets		(2)	(2)
Repurchase agreements	$ (2)
Total offsetting of financial liabilities	(2)
Gross Amount Presented in Balance Sheet [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	4	3	6
Total offsetting of financial assets	4	3	6
Repurchase agreements	6	1	4
Total offsetting of financial liabilities	6	1	4
Netting Adjustments [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(4)	(1)	(4)
Total offsetting of financial assets	(4)	(1)	(4)
Repurchase agreements	(4)	(1)	(4)
Total offsetting of financial liabilities	$ (4)	$ (1)	$ (4)