Debt and Financing Costs - Components of Financing Costs, Net (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Debt Disclosure [Abstract]
Interest expense	$ 123	$ 124	$ 251	$ 248
Amortization of deferred loan costs	2	1	4	3
Capitalized interest	(59)	(72)	(117)	(150)
Interest income	(3)	(1)	(5)	(4)
Financing costs, net	$ 63	$ 52	$ 133	$ 97