DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Assets and Liabilities Measured at Fair Value (Details) - Commodity Derivative Instruments - Recurring - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative asset, fair value	$ 84	$ 67
Derivative asset, netting	(36)	(43)
Derivative asset	48	24
Derivative liability, fair value	41	107
Derivative liability, netting	(36)	(43)
Derivative liability	5	64
Quoted Price in Active Markets (Level 1)
Derivative [Line Items]
Derivative asset, fair value	0	0
Derivative liability, fair value	0	0
Significant Other Inputs (Level 2)
Derivative [Line Items]
Derivative asset, fair value	84	67
Derivative liability, fair value	41	107
Significant Unobservable Inputs (Level 3)
Derivative [Line Items]
Derivative asset, fair value	0	0
Derivative liability, fair value	$ 0	$ 0

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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