FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Assets:
Short-term investments	$ 294	$ 470
Price risk management instruments, netting	60	115
Price risk management instruments, assets	292	284
TOTAL ASSETS	5,358	5,315
Liabilities:
Price risk management instruments, netting	(37)	(25)
TOTAL LIABILITIES	168	217
Amount primarily related to deferred taxes on appreciation of investment value	740	671
Nuclear decommissioning trusts
Assets:
Short-term investments	10	27
Global equity securities	2,542	2,398
Fixed-income securities	1,857	1,759
TOTAL ASSETS	4,437	4,209
Rabbi trusts
Assets:
Fixed-income securities	104	106
Life insurance contracts	76	79
TOTAL ASSETS	180	185
Long-term disability trust
Assets:
Short-term investments	6	9
TOTAL ASSETS	155	167
Price Risk Derivative, Electricity
Assets:
Price risk management instruments, netting	16	2
Price risk management instruments, assets	237	170
Liabilities:
Price risk management instruments, netting	(24)	(25)
Price risk management instruments, liabilities	167	214
Price Risk Derivative, Gas
Assets:
Price risk management instruments, netting	44	113
Price risk management instruments, assets	55	114
Liabilities:
Price risk management instruments, netting	(13)	0
Price risk management instruments, liabilities	1	3
Level 1
Assets:
Short-term investments	294	470
Price risk management instruments, gross subject to netting	0	0
TOTAL ASSETS	3,880	3,828
Liabilities:
TOTAL LIABILITIES	0	0
Level 1 | Nuclear decommissioning trusts
Assets:
Short-term investments	10	27
Global equity securities	2,542	2,398
Fixed-income securities	1,028	924
TOTAL ASSETS	3,580	3,349
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	6	9
TOTAL ASSETS	6	9
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	0	0
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	66	3
TOTAL ASSETS	1,075	1,023
Liabilities:
TOTAL LIABILITIES	21	4
Level 2 | Nuclear decommissioning trusts
Assets:
Short-term investments	0	0
Global equity securities	0	0
Fixed-income securities	829	835
TOTAL ASSETS	829	835
Level 2 | Rabbi trusts
Assets:
Fixed-income securities	104	106
Life insurance contracts	76	79
TOTAL ASSETS	180	185
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	55	2
Liabilities:
Price risk management instruments, gross subject to netting	7	1
Level 2 | Price Risk Derivative, Gas
Assets:
Price risk management instruments, gross subject to netting	11	1
Liabilities:
Price risk management instruments, gross subject to netting	14	3
Level 3
Assets:
Short-term investments	0	0
Price risk management instruments, gross subject to netting	166	166
TOTAL ASSETS	166	166
Liabilities:
TOTAL LIABILITIES	184	238
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	166	166
Liabilities:
Price risk management instruments, gross subject to netting	184	238
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
Assets measured at NAV | Nuclear decommissioning trusts
Assets:
Assets measured at NAV	28	25
Assets measured at NAV | Long-term disability trust
Assets:
Assets measured at NAV	$ 149	$ 158