Debt, Interest Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense	$ 557	$ 539	$ 511
Less capitalized interest	87	71	65
Interest and debt expense, net of capitalized interest	$ 470	$ 468	$ 446