Financial Instruments and Risk Management - Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value Measurements
Total current derivative contracts, assets	$ 41	$ 64
Total noncurrent derivative contracts, assets	1	6
Total current derivative contracts, liabilities	23	31
Total noncurrent derivative contracts, liabilities	87	120
Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	20	49
Total noncurrent derivative contracts, assets	1	6
Total current derivative contracts, liabilities	18	8
Total noncurrent derivative contracts, liabilities	1
Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	19	15
Total current derivative contracts, liabilities	4	21
Cross-currency and other contracts
Fair Value Measurements
Total current derivative contracts, assets	2
Total current derivative contracts, liabilities	1	2
Total noncurrent derivative contracts, liabilities	86	120
Derivatives Designated As Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	19	51
Total noncurrent derivative contracts, assets	1	6
Total current derivative contracts, liabilities	13	4
Total noncurrent derivative contracts, liabilities	87	117
Derivatives Designated As Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	18	46
Total noncurrent derivative contracts, assets	1	6
Total current derivative contracts, liabilities	13	4
Total noncurrent derivative contracts, liabilities	1
Derivatives Designated As Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	1	5
Derivatives Designated As Hedging Instruments | Cross-currency and other contracts
Fair Value Measurements
Total noncurrent derivative contracts, liabilities	86	117
Derivatives Not Designated as Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	22	13
Total current derivative contracts, liabilities	10	27
Total noncurrent derivative contracts, liabilities		3
Derivatives Not Designated as Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	2	3
Total current derivative contracts, liabilities	5	4
Derivatives Not Designated as Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	18	10
Total current derivative contracts, liabilities	4	21
Derivatives Not Designated as Hedging Instruments | Cross-currency and other contracts
Fair Value Measurements
Total current derivative contracts, assets	2
Total current derivative contracts, liabilities	$ 1	2
Total noncurrent derivative contracts, liabilities		$ 3