FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets:
Short-term investments		$ 385
Derivative Asset	$ 131	139
TOTAL ASSETS	3,723	4,145
Liabilities:
Price risk management instruments, netting	(34)
TOTAL LIABILITIES	86	88
Amount primarily related to deferred taxes on appreciation of investment value	440	440
Nuclear decommissioning trusts
Assets:
Short-term investments	28	23
Global equity securities	1,862	1,967
Fixed-income securities	1,375	1,295
Assets measured at NAV	17	18
TOTAL ASSETS	3,282	3,303
Rabbi trusts
Assets:
Fixed-income securities	74	72
Life insurance contracts	69	71
TOTAL ASSETS	143	143
Long-term disability trust
Assets:
Short-term investments	5	8
Assets measured at NAV	162	167
TOTAL ASSETS	167	175
Price Risk Derivative, Electricity
Assets:
Price risk management instruments, netting	3	6
Derivative Asset	130	138
Liabilities:
Price risk management instruments, netting	(33)	(25)
Derivative Liability	85	87
Price Risk Derivative, Gas
Assets:
Derivative Asset	1	1
Liabilities:
Price risk management instruments, netting	(1)	0
Derivative Liability	1	1
Level 1
Assets:
Short-term investments		385
Derivative Asset	0	0
TOTAL ASSETS	2,671	3,116
Liabilities:
TOTAL LIABILITIES	8	10
Level 1 | Nuclear decommissioning trusts
Assets:
Short-term investments	28	23
Global equity securities	1,862	1,967
Fixed-income securities	776	733
TOTAL ASSETS	2,666	2,723
Level 1 | Rabbi trusts
Assets:
Fixed-income securities	0	0
Life insurance contracts	0	0
TOTAL ASSETS	0	0
Level 1 | Long-term disability trust
Assets:
Short-term investments	5	8
TOTAL ASSETS	5	8
Level 1 | Price Risk Derivative, Electricity
Assets:
Price risk management instruments, gross subject to netting	0	0
Liabilities:
Price risk management instruments, gross subject to netting	8	10
Level 1 | Price Risk Derivative, Gas
Assets:
Derivative Asset	0	0
Liabilities:
Price risk management instruments, gross subject to netting	0	0
Level 2
Assets:
Short-term investments		0
Derivative Asset	3	4
TOTAL ASSETS	745	709
Liabilities:
TOTAL LIABILITIES	27	16
Level 2 | Nuclear decommissioning trusts
Assets:
Short-term investments	0	0
Global equity securities	0	0
Fixed-income securities	599	562
TOTAL ASSETS	599	562
Level 2 | Rabbi trusts
Assets:
Fixed-income securities	74	72
Life insurance contracts	69	71
TOTAL ASSETS	143	143
Level 2 | Long-term disability trust
Assets:
Short-term investments	0	0
TOTAL ASSETS	0	0
Level 2 | Price Risk Derivative, Electricity
Assets:
Price risk management instruments, gross subject to netting	2	3
Liabilities:
Price risk management instruments, gross subject to netting	25	15
Level 2 | Price Risk Derivative, Gas
Assets:
Derivative Asset	1	1
Liabilities:
Price risk management instruments, gross subject to netting	2	1
Level 3
Assets:
Short-term investments		0
Derivative Asset	125	129
TOTAL ASSETS	125	129
Liabilities:
TOTAL LIABILITIES	85	87
Level 3 | Nuclear decommissioning trusts
Assets:
Short-term investments	0	0
Global equity securities	0	0
Fixed-income securities	0	0
TOTAL ASSETS	0	0
Level 3 | Rabbi trusts
Assets:
Fixed-income securities	0	0
Life insurance contracts	0	0
TOTAL ASSETS	0	0
Level 3 | Long-term disability trust
Assets:
Short-term investments	0	0
TOTAL ASSETS	0	0
Level 3 | Price Risk Derivative, Electricity
Assets:
Price risk management instruments, gross subject to netting	125	129
Liabilities:
Price risk management instruments, gross subject to netting	85	87
Level 3 | Price Risk Derivative, Gas
Assets:
Derivative Asset	0	0
Liabilities:
Price risk management instruments, gross subject to netting	$ 0	$ 0