Debt and Financing Costs - Components of Financing Costs, Net (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Disclosure [Abstract]
Interest expense		$ 115	$ 116	$ 231	$ 232
Amortization of deferred loan costs		2	2	4	3
Capitalized interest		(13)	(12)	(27)	(23)
Loss on extinguishment of debt	$ 1	0	0	1	0
Interest income		(5)	(2)	(10)	(3)
Financing costs, net		$ 99	$ 104	$ 199	$ 209