FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets:
Short-term investments	$ 377	$ 385
Price risk management instruments, netting	3	6
Derivative Asset	125	139
TOTAL ASSETS	4,137	4,145
Liabilities:
Price risk management instruments, netting	(18)	(25)
TOTAL LIABILITIES	88	88
Amount primarily related to deferred taxes on appreciation of investment value	455	440
Nuclear decommissioning trusts
Assets:
Short-term investments	14	23
Global equity securities	1,970	1,967
Fixed-income securities	1,369	1,295
TOTAL ASSETS	3,372	3,303
Rabbi trusts
Assets:
Fixed-income securities	75	72
Life insurance contracts	68	71
TOTAL ASSETS	143	143
Long-term disability trust
Assets:
Short-term investments	8	8
TOTAL ASSETS	120	175
Price Risk Derivative, Electricity
Assets:
Price risk management instruments, netting	2	6
Derivative Asset	118	138
Liabilities:
Price risk management instruments, netting	(17)	(25)
Derivative Liability	86	87
Price Risk Derivative, Gas
Assets:
Price risk management instruments, netting	1	0
Derivative Asset	7	1
Liabilities:
Price risk management instruments, netting	(1)	0
Derivative Liability	2	1
Level 1
Assets:
Short-term investments	377	385
Price risk management instruments, gross subject to netting	1	0
TOTAL ASSETS	3,108	3,116
Liabilities:
TOTAL LIABILITIES	5	10
Level 1 | Nuclear decommissioning trusts
Assets:
Short-term investments	14	23
Global equity securities	1,970	1,967
Fixed-income securities	738	733
TOTAL ASSETS	2,722	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	8	8
TOTAL ASSETS	8	8
Level 1 | Price Risk Derivative, Electricity
Assets:
Price risk management instruments, gross subject to netting	1	0
Liabilities:
Price risk management instruments, gross subject to netting	5	10
Level 1 | Price Risk Derivative, Gas
Assets:
Price risk management instruments, gross subject to netting	0	0
Liabilities:
Price risk management instruments, gross subject to netting	0	0
Level 2
Assets:
Short-term investments	0	0
Price risk management instruments, gross subject to netting	11	4
TOTAL ASSETS	785	709
Liabilities:
TOTAL LIABILITIES	15	16
Level 2 | Nuclear decommissioning trusts
Assets:
Short-term investments	0	0
Global equity securities	0	0
Fixed-income securities	631	562
TOTAL ASSETS	631	562
Level 2 | Rabbi trusts
Assets:
Fixed-income securities	75	72
Life insurance contracts	68	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	5	3
Liabilities:
Price risk management instruments, gross subject to netting	12	15
Level 2 | Price Risk Derivative, Gas
Assets:
Price risk management instruments, gross subject to netting	6	1
Liabilities:
Price risk management instruments, gross subject to netting	3	1
Level 3
Assets:
Short-term investments	0	0
Price risk management instruments, gross subject to netting	110	129
TOTAL ASSETS	110	129
Liabilities:
TOTAL LIABILITIES	86	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	110	129
Liabilities:
Price risk management instruments, gross subject to netting	86	87
Level 3 | Price Risk Derivative, Gas
Assets:
Price risk management instruments, gross subject to netting	0	0
Liabilities:
Price risk management instruments, gross subject to netting	0	0
Fair Value Measured at Net Asset Value | Nuclear decommissioning trusts
Assets:
Assets measured at NAV	19	18
Fair Value Measured at Net Asset Value | Long-term disability trust
Assets:
Assets measured at NAV	$ 112	$ 167