Debt and Capital Lease Obligations, Interest Incurred (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense	$ 144	$ 134	$ 283	$ 268
Less capitalized interest	20	15	38	28
Interest and debt expense, net of capitalized interest	$ 124	$ 119	$ 245	$ 240