Financial Instruments and Risk Management - Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value Measurements
Total current derivative contracts, assets	$ 87	$ 40
Total noncurrent derivative contracts, assets	43	46
Total current derivative contracts, liabilities	21	25
Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	66	18
Total noncurrent derivative contracts, assets	15	7
Total current derivative contracts, liabilities	15	3
Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	21	1
Total noncurrent derivative contracts, assets	1
Total current derivative contracts, liabilities	5	22
Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, assets		21
Total noncurrent derivative contracts, assets	27	39
Total current derivative contracts, liabilities	1
Derivatives Designated As Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	63	18
Total noncurrent derivative contracts, assets	43	46
Total current derivative contracts, liabilities	14	3
Derivatives Designated As Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	63	17
Total noncurrent derivative contracts, assets	15	7
Total current derivative contracts, liabilities	14	3
Derivatives Designated As Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets		1
Total noncurrent derivative contracts, assets	1
Derivatives Designated As Hedging Instruments | Interest rate and other contracts
Fair Value Measurements
Total noncurrent derivative contracts, assets	27	39
Derivatives Not Designated As Hedging Instruments
Fair Value Measurements
Total current derivative contracts, assets	24	22
Total current derivative contracts, liabilities	7	22
Derivatives Not Designated As Hedging Instruments | Commodity contracts
Fair Value Measurements
Total current derivative contracts, assets	3	1
Total current derivative contracts, liabilities	1
Derivatives Not Designated As Hedging Instruments | Foreign currency contracts
Fair Value Measurements
Total current derivative contracts, assets	21
Total current derivative contracts, liabilities	5	22
Derivatives Not Designated As Hedging Instruments | Interest rate and other contracts
Fair Value Measurements
Total current derivative contracts, assets		$ 21
Total current derivative contracts, liabilities	$ 1