FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Financial Instruments Measured at Fair Value on a Recurring Basis) (Details) - Recurring - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash Equivalents	$ 15	$ 30
Restricted Cash	10	12
Energy Derivative Contract Assets - Regulatory Recovery	5	9
Energy Derivative Contract Assets - No Regulatory Recovery	4	3
Total Assets	34	54
Liabilities
Energy Derivative Contract Liabilities - Regulatory Recovery	(48)	(26)
Energy Derivative Contracts, No Regulatory Recovery		(1)
Interest Rate Swap		(1)
Total Liabilities	(48)	(28)
Total Assets (Liabilities), Net	(14)	26
Level 1
Assets
Cash Equivalents	15	30
Restricted Cash	10	12
Energy Derivative Contract Assets - Regulatory Recovery	0	0
Energy Derivative Contract Assets - No Regulatory Recovery	0	0
Total Assets	25	42
Liabilities
Energy Derivative Contract Liabilities - Regulatory Recovery	0	0
Energy Derivative Contracts, No Regulatory Recovery		0
Interest Rate Swap		0
Total Liabilities	0	0
Total Assets (Liabilities), Net	25	42
Level 2
Assets
Cash Equivalents	0	0
Restricted Cash	0	0
Energy Derivative Contract Assets - Regulatory Recovery	5	9
Energy Derivative Contract Assets - No Regulatory Recovery	0	0
Total Assets	5	9
Liabilities
Energy Derivative Contract Liabilities - Regulatory Recovery	(44)	(26)
Energy Derivative Contracts, No Regulatory Recovery		0
Interest Rate Swap		(1)
Total Liabilities	(44)	(27)
Total Assets (Liabilities), Net	(39)	(18)
Level 3
Assets
Cash Equivalents	0	0
Restricted Cash	0	0
Energy Derivative Contract Assets - Regulatory Recovery	0	0
Energy Derivative Contract Assets - No Regulatory Recovery	4	3
Total Assets	4	3
Liabilities
Energy Derivative Contract Liabilities - Regulatory Recovery	(4)	0
Energy Derivative Contracts, No Regulatory Recovery		(1)
Interest Rate Swap		0
Total Liabilities	(4)	(1)
Total Assets (Liabilities), Net	$ 0	$ 2