Financial Instruments and Risk Management - Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value Measurements
Total current derivative contracts, assets	$ 52	$ 40
Total noncurrent derivative contracts, assets	7	46
Total current derivative contracts, liabilities	31	25
Total noncurrent derivative contracts, liabilities	96
Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	40	18
Total noncurrent derivative contracts, assets	6	7
Total current derivative contracts, liabilities	14	3
Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	10	1
Total current derivative contracts, liabilities	17	22
Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, assets	2	21
Total noncurrent derivative contracts, assets	1	39
Derivatives Designated As Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	41	18
Total noncurrent derivative contracts, assets	7	46
Total current derivative contracts, liabilities	14	3
Total noncurrent derivative contracts, liabilities	96
Derivatives Designated As Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	38	17
Total noncurrent derivative contracts, assets	6	7
Total current derivative contracts, liabilities	13	3
Derivatives Designated As Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	3	1
Total current derivative contracts, liabilities	1
Derivatives Designated As Hedging Instruments | Interest rate and other contracts
Fair Value Measurements
Total noncurrent derivative contracts, assets	1	39
Derivatives Not Designated as Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	11	22
Total current derivative contracts, liabilities	17	22
Derivatives Not Designated as Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	2	1
Total current derivative contracts, liabilities	1
Derivatives Not Designated as Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	7
Total current derivative contracts, liabilities	16	22
Derivatives Not Designated as Hedging Instruments | Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, assets	$ 2	$ 21