FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets:
Short-term investments	$ 411	$ 470
Price risk management instruments, netting	90	115
Price risk management instruments, assets	363	284
TOTAL ASSETS	5,510	5,315
Liabilities:
Price risk management instruments, netting	(22)	(25)
TOTAL LIABILITIES	237	217
Amount primarily related to deferred taxes on appreciation of investment value	740	671
Nuclear decommissioning trusts
Assets:
Short-term investments	25	27
Global equity securities	2,478	2,398
Fixed-income securities	1,879	1,759
TOTAL ASSETS	4,410	4,209
Rabbi trusts
Assets:
Fixed-income securities	104	106
Life insurance contracts	77	79
TOTAL ASSETS	181	185
Long-term disability trust
Assets:
Short-term investments	6	9
TOTAL ASSETS	145	167
Price Risk Derivative, Electricity
Assets:
Price risk management instruments, netting	13	2
Price risk management instruments, assets	216	170
Liabilities:
Price risk management instruments, netting	(17)	(25)
Price risk management instruments, liabilities	230	214
Price Risk Derivative, Gas
Assets:
Price risk management instruments, netting	77	113
Price risk management instruments, assets	147	114
Liabilities:
Price risk management instruments, netting	(5)	0
Price risk management instruments, liabilities	7	3
Level 1
Assets:
Short-term investments	411	470
Price risk management instruments, gross subject to netting	0	0
TOTAL ASSETS	3,974	3,828
Liabilities:
TOTAL LIABILITIES	0	0
Level 1 | Nuclear decommissioning trusts
Assets:
Short-term investments	25	27
Global equity securities	2,478	2,398
Fixed-income securities	1,054	924
TOTAL ASSETS	3,557	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	110	3
TOTAL ASSETS	1,116	1,023
Liabilities:
TOTAL LIABILITIES	16	4
Level 2 | Nuclear decommissioning trusts
Assets:
Short-term investments	0	0
Global equity securities	0	0
Fixed-income securities	825	835
TOTAL ASSETS	825	835
Level 2 | Rabbi trusts
Assets:
Fixed-income securities	104	106
Life insurance contracts	77	79
TOTAL ASSETS	181	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	40	2
Liabilities:
Price risk management instruments, gross subject to netting	4	1
Level 2 | Price Risk Derivative, Gas
Assets:
Price risk management instruments, gross subject to netting	70	1
Liabilities:
Price risk management instruments, gross subject to netting	12	3
Level 3
Assets:
Short-term investments	0	0
Price risk management instruments, gross subject to netting	163	166
TOTAL ASSETS	163	166
Liabilities:
TOTAL LIABILITIES	243	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	163	166
Liabilities:
Price risk management instruments, gross subject to netting	243	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	$ 139	$ 158