Debt, Interest Incurred (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense	$ 136	$ 144	$ 272	$ 283
Less capitalized interest	24	20	48	38
Interest and debt expense, net of capitalized interest	$ 112	$ 124	$ 224	$ 245