Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Expense [Abstract]
Interest expense before capitalization	$ 335	$ 358	$ 398
Capitalized interest	(14)	(23)	(26)
Interest Expense	321	335	372
Interest paid, net	$ 331	$ 314	$ 351