FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 470	$ 1,323
Total nuclear decommissioning trusts	4,209	3,703
Rabbi trusts	185	173
Long-term disability trust	167	166
Netting		(8)
Netting	(115)
Total assets	5,315	5,523
Netting	(25)	(14)
Amount primarily related to deferred taxes on appreciation of investment value	671	530
Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Netting		(11)
Netting	(2)
Netting	(25)	(13)
Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Netting	(113)	(3)
Netting	0	(1)
Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	27	6
Long-term disability trust	9	10
Global equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	2,398	2,086
Fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	1,759	1,590
Rabbi trusts	106	100
Price risk management instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	284	158
TOTAL LIABILITIES	217	147
Price risk management instruments | Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	170	152
TOTAL LIABILITIES	214	146
Price risk management instruments | Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	114	6
TOTAL LIABILITIES	3	1
Life insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rabbi trusts	79	73
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	470	1,323
Total nuclear decommissioning trusts	3,349	2,954
Rabbi trusts	0	0
Long-term disability trust	9	10
Total assets	3,828	4,287
Level 1 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	27	6
Long-term disability trust	9	10
Level 1 | Global equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	2,398	2,086
Level 1 | Fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	924	862
Rabbi trusts	0	0
Level 1 | Price risk management instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	0	0
TOTAL LIABILITIES	0	1
Level 1 | Price risk management instruments | Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	0	0
TOTAL LIABILITIES	0	1
Level 1 | Price risk management instruments | Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	0	0
TOTAL LIABILITIES	0	0
Level 1 | Life insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rabbi trusts	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Total nuclear decommissioning trusts	835	728
Rabbi trusts	185	173
Long-term disability trust	0	0
Total assets	1,023	906
Level 2 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	0	0
Long-term disability trust	0	0
Level 2 | Global equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	0	0
Level 2 | Fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	835	728
Rabbi trusts	106	100
Level 2 | Price risk management instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	3	5
TOTAL LIABILITIES	4	4
Level 2 | Price risk management instruments | Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	2	2
TOTAL LIABILITIES	1	2
Level 2 | Price risk management instruments | Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	1	3
TOTAL LIABILITIES	3	2
Level 2 | Life insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rabbi trusts	79	73
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	0	0
Total nuclear decommissioning trusts	0	0
Rabbi trusts	0	0
Long-term disability trust	0	0
Total assets	166	161
Level 3 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	0	0
Long-term disability trust	0	0
Level 3 | Global equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	0	0
Level 3 | Fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	0	0
Rabbi trusts	0	0
Level 3 | Price risk management instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	166	161
TOTAL LIABILITIES	238	156
Level 3 | Price risk management instruments | Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	166	161
TOTAL LIABILITIES	238	156
Level 3 | Price risk management instruments | Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	0	0
TOTAL LIABILITIES	0	0
Level 3 | Life insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rabbi trusts	0	0
Assets measured at NAV
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	25	21
Long-term disability trust	$ 158	$ 156