Financial Instruments and Risk Management - Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value Measurements
Total current derivative contracts, assets	$ 70	$ 64
Total noncurrent derivative contracts, assets	3	6
Total current derivative contracts, liabilities	17	31
Total noncurrent derivative contracts, liabilities	94	120
Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	46	49
Total noncurrent derivative contracts, assets	3	6
Total current derivative contracts, liabilities	7	8
Total noncurrent derivative contracts, liabilities	2
Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	24	15
Total current derivative contracts, liabilities	6	21
Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, liabilities	4	2
Total noncurrent derivative contracts, liabilities	92	120
Derivatives Designated As Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	41	51
Total noncurrent derivative contracts, assets	3	6
Total current derivative contracts, liabilities	4	4
Total noncurrent derivative contracts, liabilities	94	117
Derivatives Designated As Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	40	46
Total noncurrent derivative contracts, assets	3	6
Total current derivative contracts, liabilities	3	4
Total noncurrent derivative contracts, liabilities	2
Derivatives Designated As Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	1	5
Total current derivative contracts, liabilities	1
Derivatives Designated As Hedging Instruments | Interest rate and other contracts
Fair Value Measurements
Total noncurrent derivative contracts, liabilities	92	117
Derivatives Not Designated as Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	29	13
Total current derivative contracts, liabilities	13	27
Total noncurrent derivative contracts, liabilities		3
Derivatives Not Designated as Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	6	3
Total current derivative contracts, liabilities	4	4
Derivatives Not Designated as Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	23	10
Total current derivative contracts, liabilities	5	21
Derivatives Not Designated as Hedging Instruments | Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, liabilities	$ 4	2
Total noncurrent derivative contracts, liabilities		$ 3