Securities Financing Activities - Summarized Securities Financing Agreements (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Securities Financing Transaction [Line Items]
Reverse repurchase agreements			$ 10
Total offsetting of financial assets			10
Collateral [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements		(2)	(126)
Securities borrowed			(3)
Total offsetting of financial assets		(2)	(129)
Repurchase agreements	(2)		(262)
Total offsetting of financial liabilities	(2)		(262)
Gross Amount Presented in Balance Sheet [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	2	3	442
Securities borrowed			3
Total offsetting of financial assets	2	3	445
Repurchase agreements	4	1	568
Total offsetting of financial liabilities	4	1	568
Netting Adjustments [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(2)	(1)	(306)
Total offsetting of financial assets	(2)	(1)	(306)
Repurchase agreements	(2)	(1)	(306)
Total offsetting of financial liabilities	$ (2)	$ (1)	$ (306)