Securities Financing Activities - Summarized Securities Financing Agreements (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Securities Financing Transaction [Line Items]
Reverse repurchase agreements		$ 3
Total offsetting of financial assets		3
Collateral [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(2)	(66)
Securities borrowed		(12)
Total offsetting of financial assets	(2)	(78)
Repurchase agreements		(239)
Total offsetting of financial liabilities		(239)
Gross Amount Presented in Balance Sheet [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	3	347
Securities borrowed		12
Total offsetting of financial assets	3	359
Repurchase agreements	1	517
Total offsetting of financial liabilities	1	517
Netting Adjustments [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(1)	(278)
Total offsetting of financial assets	(1)	(278)
Repurchase agreements	(1)	(278)
Total offsetting of financial liabilities	$ (1)	$ (278)