Debt, Interest Incurred (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense	$ 133	$ 134	$ 405	$ 417
Less capitalized interest	22	23	70	61
Interest and debt expense, net of capitalized interest	$ 111	$ 111	$ 335	$ 356