Debt and Capital Lease Obligations, Interest Incurred (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense	$ 134	$ 134	$ 417	$ 402
Less capitalized interest	23	20	61	48
Interest and debt expense, net of capitalized interest	$ 111	$ 114	$ 356	$ 354