Derivatives and Hedging Activities - Credit Derivatives Sold and Held (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Credit Derivatives [Line Items]
Notional Amount	$ 13	$ 68	$ 11
Single Name Credit Default Swaps [Member]
Credit Derivatives [Line Items]
Notional Amount	5	55	5
Average Term (Years)	5 months 19 days	6 months 7 days	8 months 19 days
Payment / Performance Risk	0.87%	22.28%	0.87%
Other [Member]
Credit Derivatives [Line Items]
Notional Amount	$ 8	$ 13	$ 6
Average Term (Years)	3 years 15 days	4 years 9 months 18 days	2 years 10 months 21 days
Payment / Performance Risk	9.39%	8.23%	9.58%