Debt - Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Debt Disclosure [Abstract]
Total interest cost	$ 198	$ 168	$ 581	$ 469
Capitalized interest	(74)	(102)	(225)	(370)
Total interest expense, net	$ 124	$ 66	$ 356	$ 99