FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets:
Short-term investments	$ 473	$ 385
Price risk management instruments, netting	2	6
Derivative Asset	121	139
TOTAL ASSETS	4,159	4,145
Liabilities:
Price risk management instruments, netting	(26)	(25)
TOTAL LIABILITIES	80	88
Amount primarily related to deferred taxes on appreciation of investment value	436	440
Nuclear decommissioning trusts
Assets:
Short-term investments	22	23
Global equity securities	1,873	1,967
Fixed-income securities	1,351	1,295
TOTAL ASSETS	3,264	3,303
Rabbi trusts
Assets:
Fixed-income securities	74	72
Life insurance contracts	68	71
TOTAL ASSETS	142	143
Long-term disability trust
Assets:
Short-term investments	4	8
TOTAL ASSETS	159	175
Price Risk Derivative, Electricity
Assets:
Price risk management instruments, netting	1	6
Derivative Asset	117	138
Liabilities:
Price risk management instruments, netting	(26)	(25)
Derivative Liability	79	87
Price Risk Derivative, Gas
Assets:
Price risk management instruments, netting	1
Derivative Asset	4	1
Liabilities:
Derivative Liability	1	1
Level 1
Assets:
Short-term investments	473	385
Derivative Asset	1	0
TOTAL ASSETS	3,140	3,116
Liabilities:
TOTAL LIABILITIES	6	10
Level 1 | Nuclear decommissioning trusts
Assets:
Short-term investments	22	23
Global equity securities	1,873	1,967
Fixed-income securities	767	733
TOTAL ASSETS	2,662	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	4	8
TOTAL ASSETS	4	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	6	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	0
Derivative Asset	5	4
TOTAL ASSETS	731	709
Liabilities:
TOTAL LIABILITIES	21	16
Level 2 | Nuclear decommissioning trusts
Assets:
Short-term investments	0	0
Global equity securities	0	0
Fixed-income securities	584	562
TOTAL ASSETS	584	562
Level 2 | Rabbi trusts
Assets:
Fixed-income securities	74	72
Life insurance contracts	68	71
TOTAL ASSETS	142	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	20	15
Level 2 | Price Risk Derivative, Gas
Assets:
Derivative Asset	3	1
Liabilities:
Price risk management instruments, gross subject to netting	1	1
Level 3
Assets:
Short-term investments	0	0
Derivative Asset	113	129
TOTAL ASSETS	113	129
Liabilities:
TOTAL LIABILITIES	79	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	113	129
Liabilities:
Price risk management instruments, gross subject to netting	79	87
Level 3 | Price Risk Derivative, Gas
Assets:
Derivative Asset	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	18	18
Fair Value Measured at Net Asset Value | Long-term disability trust
Assets:
Assets measured at NAV	$ 155	$ 167