Derivatives and Risk Management - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivative
Total derivative contracts, net	$ (165)	$ (291)
Prepaid Expenses and Other
Derivative
Net derivative contracts, assets	1	31
Other Noncurrent Assets
Derivative
Net derivative contracts, assets	0	6
Other Accrued Liabilities
Derivative
Net derivative contracts, liabilities	(140)	(326)
Other Noncurrent Liabilities
Derivative
Net derivative contracts, liabilities	$ (26)	$ (2)