FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 1,323	$ 1,593
Total nuclear decommissioning trusts	3,703	3,138
Rabbi trusts	173	160
Long-term disability trust	166	162
Derivative asset, netting	(8)	88
Total assets	5,523	5,350
Derivative liability, netting	(14)	(10)
Amount primarily related to deferred taxes on appreciation of investment value	530	408
Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, netting	(11)	51
Derivative liability, netting	(13)	(10)
Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, netting	3	37
Derivative liability, netting	(1)	0
Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	6	29
Long-term disability trust	10	7
Global equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	2,086	1,793
Fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	1,590	1,300
Rabbi trusts	100	93
Price risk management instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	158	297
TOTAL LIABILITIES	147	109
Price risk management instruments | Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	152	259
TOTAL LIABILITIES	146	107
Price risk management instruments | Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	6	38
TOTAL LIABILITIES	1	2
Life insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rabbi trusts	73	67
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	1,323	1,593
Total nuclear decommissioning trusts	2,954	2,483
Rabbi trusts	0	0
Long-term disability trust	10	7
Total assets	4,287	4,083
Level 1 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	6	29
Long-term disability trust	10	7
Level 1 | Global equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	2,086	1,793
Level 1 | Fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	862	661
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	1	4
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	1	4
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	728	639
Rabbi trusts	173	160
Long-term disability trust	0	0
Total assets	906	805
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	728	639
Rabbi trusts	100	93
Level 2 | Price risk management instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	5	6
TOTAL LIABILITIES	4	7
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	5
TOTAL LIABILITIES	2	5
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	3	1
TOTAL LIABILITIES	2	2
Level 2 | Life insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rabbi trusts	73	67
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	161	203
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	161	203
TOTAL LIABILITIES	156	108
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	161	203
TOTAL LIABILITIES	156	108
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	21	16
Long-term disability trust	$ 156	$ 155