Debt and Capital Lease Obligations, Interest Incurred (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense	$ 134	$ 129	$ 402	$ 387
Less capitalized interest	20	14	48	53
Interest and debt expense, net of capitalized interest	$ 114	$ 115	$ 354	$ 334