Debt, Interest Incurred (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense	$ 136	$ 139
Less capitalized interest	24	18
Interest and debt expense, net of capitalized interest	$ 112	$ 121