Securities Financing Activities - Summarized Securities Financing Agreements (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Counterparty and Cash Collateral Netting [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements		$ (1)
Total offsetting of financial assets		(1)
Repurchase agreements			$ (1)
Total offsetting of financial liabilities			(1)
Gross Amount Presented in Balance Sheet [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	$ 1	1	3
Total offsetting of financial assets	1	$ 1	3
Repurchase agreements	1		4
Total offsetting of financial liabilities	1		4
Netting Adjustments [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(1)		(3)
Total offsetting of financial assets	(1)		(3)
Repurchase agreements	(1)		(3)
Total offsetting of financial liabilities	$ (1)		$ (3)