FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Potential Offset of Counterparty Netting and Cash Collateral) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Energy Derivative
Derivative Asset [Abstract]
Derivative Asset, Gross Amount Recognized in the Balance Sheets	$ 12	$ 12
Derivative Asset, Counterparty Netting	11	10
Collateral Received	0	0
Derivative Asset, Net Amount	1	2
Derivative Liability [Abstract]
Derivative Liability, Fair Value, Gross Liability	(37)	(27)
Derivative Liability, Counterparty Netting	(11)	(10)
Derivative, Collateral, Right to Reclaim Cash	0	0
Derivative Liability, Net Amount	$ (26)	(17)
Interest Rate Swap
Derivative Liability [Abstract]
Derivative Liability, Fair Value, Gross Liability		(1)
Derivative Liability, Counterparty Netting		0
Derivative, Collateral, Right to Reclaim Cash		0
Derivative Liability, Net Amount		$ (1)

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