FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Financial Instruments Measured at Fair Value on a Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash Equivalents	$ 30	$ 23
Restricted Cash	12	7
Energy Derivative Contract Assets - Regulatory Recovery	9	3
Energy Derivative Contract Assets - No Regulatory Recovery	3	2
Total Assets	54	35
Liabilities
Energy Derivative Contract Liabilities - Regulatory Recovery	(26)	(3)
Derivative Liabilities - No Regulatory Recovery	(1)
Interest Rate Swap	(1)	(2)
Total Liabilities	(28)	(5)
Net Total Assets (Liabilities)	26	30
Level 1
Assets
Cash Equivalents	30	23
Restricted Cash	12	7
Energy Derivative Contract Assets - Regulatory Recovery	0	0
Energy Derivative Contract Assets - No Regulatory Recovery	0	0
Total Assets	42	30
Liabilities
Energy Derivative Contract Liabilities - Regulatory Recovery	0	0
Derivative Liabilities - No Regulatory Recovery	0
Interest Rate Swap	0	0
Total Liabilities	0	0
Net Total Assets (Liabilities)	42	30
Level 2
Assets
Cash Equivalents	0	0
Restricted Cash	0	0
Energy Derivative Contract Assets - Regulatory Recovery	9	3
Energy Derivative Contract Assets - No Regulatory Recovery	0	0
Total Assets	9	3
Liabilities
Energy Derivative Contract Liabilities - Regulatory Recovery	(26)	(2)
Derivative Liabilities - No Regulatory Recovery	0
Interest Rate Swap	(1)	(2)
Total Liabilities	(27)	(4)
Net Total Assets (Liabilities)	(18)	(1)
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	3	2
Total Assets	3	2
Liabilities
Energy Derivative Contract Liabilities - Regulatory Recovery	0	(1)
Derivative Liabilities - No Regulatory Recovery	(1)
Interest Rate Swap	0	0
Total Liabilities	(1)	(1)
Net Total Assets (Liabilities)	$ 2	$ 1