FAIR VALUE MEASUREMENTS (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 1,593	$ 385
Total nuclear decommissioning trusts	3,138	3,303
Rabbi trusts	160	143
Long-term disability trust	162	175
Derivative asset, netting	88	6
Total assets	5,350	4,145
Derivative liability, netting	(10)	(25)
Amount primarily related to deferred taxes on appreciation of investment value	408	440
Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, netting	51	6
Derivative liability, netting	(10)	(25)
Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, netting	37	0
Derivative liability, netting	0	0
Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	29	23
Long-term disability trust	7	8
Global equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	1,793	1,967
Fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	1,300	1,295
Rabbi trusts	93	72
Price risk management instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	297	139
TOTAL LIABILITIES	109	88
Price risk management instruments | Electric
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	259	138
TOTAL LIABILITIES	107	87
Price risk management instruments | Gas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	38	1
TOTAL LIABILITIES	2	1
Life insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rabbi trusts	67	71
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	1,593	385
Total nuclear decommissioning trusts	2,483	2,723
Rabbi trusts	0	0
Long-term disability trust	7	8
Total assets	4,083	3,116
Level 1 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	29	23
Long-term disability trust	7	8
Level 1 | Global equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	1,793	1,967
Level 1 | Fixed-income securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	661	733
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	4	10
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	4	10
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	639	562
Rabbi trusts	160	143
Long-term disability trust	0	0
Total assets	805	709
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	639	562
Rabbi trusts	93	72
Level 2 | Price risk management instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total price risk management instruments	6	4
TOTAL LIABILITIES	7	16
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	5	3
TOTAL LIABILITIES	5	15
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	1
TOTAL LIABILITIES	2	1
Level 2 | Life insurance contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rabbi trusts	67	71
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	203	129
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	203	129
TOTAL LIABILITIES	108	87
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	203	129
TOTAL LIABILITIES	108	87
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
NAV
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total nuclear decommissioning trusts	16	18
Long-term disability trust	$ 155	$ 167