Derivatives and Risk Management - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative
Total derivative contracts, net	$ (35)	$ (83)
Prepaid Expenses and Other
Derivative
Net derivative contracts, assets	21	0
Other Noncurrent Assets
Derivative
Net derivative contracts, assets	1	1
Other Accrued Liabilities
Derivative
Net derivative contracts, liabilities	(31)	(68)
Other Noncurrent Liabilities
Derivative
Net derivative contracts, liabilities	$ (26)	$ (16)