Income Taxes - Valuation Allowances Rollforward (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Balance at January 1				$ (555,000,000)
Valuation Allowance [Line Items]
Balance at December 31	(864,000,000)	(818,000,000)	(922,000,000)	(555,000,000)
Additions [Member]
Valuation Allowance [Line Items]
Change in valuation allowances	(59,000,000)	(38,000,000)	(426,000,000)
Reductions [Member]
Valuation Allowance [Line Items]
Change in valuation allowances	$ 13,000,000	$ 142,000,000	$ 59,000,000