DERIVATIVES - Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Gross and net fair values of outstanding derivatives (in millions)
Collateral received netted against derivative assets	$ 0	$ 4
Collateral paid netted against derivative liabilities	54	13
Collateral deposited with clearinghouses and brokers	53	25
Cash-flow hedges | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Total net fair value, asset	3	1
Cash-flow hedges | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Total net fair value, liability		6
Cash-flow hedges | Level 2 | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	3	1
Cash-flow hedges | Level 2 | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		6
Not designated as hedging instruments | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(517)	(196)
Total net fair value, asset	195	27
Not designated as hedging instruments | Commodity contracts | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(1)	(2)
Total net fair value, asset	2	3
Not designated as hedging instruments | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(517)	(196)
Total net fair value, liability	240	27
Not designated as hedging instruments | Commodity contracts | Deferred credits and liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(1)	(2)
Total net fair value, liability	3	5
Not designated as hedging instruments | Level 1 | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	485	166
Not designated as hedging instruments | Level 1 | Commodity contracts | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	1	2
Not designated as hedging instruments | Level 1 | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	535	172
Not designated as hedging instruments | Level 1 | Commodity contracts | Deferred credits and liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	1	1
Not designated as hedging instruments | Level 2 | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	227	57
Not designated as hedging instruments | Level 2 | Commodity contracts | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	2	3
Not designated as hedging instruments | Level 2 | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	222	51
Not designated as hedging instruments | Level 2 | Commodity contracts | Deferred credits and liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	$ 3	$ 6