Debt, Interest Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense incurred	$ 511	$ 504	$ 467
Less capitalized interest	65	71	70
Interest and debt expense, net of capitalized interest	$ 446	$ 433	$ 397