Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest Expense [Abstract]
Interest expense before capitalization	$ 398	$ 457	$ 468
Capitalized interest	(26)	(19)	(24)
Interest expense	$ 372	$ 438	$ 444