Debt and Capital Lease Obligations, Interest Incurred (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Interest and Debt Expense, Net of Capitalized Interest
Interest and debt expense	$ 134	$ 130	$ 268	$ 258
Less capitalized interest	15	19	28	39
Interest and debt expense, net of capitalized interest	$ 119	$ 111	$ 240	$ 219