FAIR VALUE MEASUREMENTS (Level 3 Measurements and Sensitivity Analysis) (Details) $ in Millions	Sep. 30, 2026 USD ($) $ / shares	Dec. 31, 2025 USD ($) $ / shares
Market approach \| Congestion revenue rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets \| $	$ 190	$ 252
Liabilities \| $	54	83
Discounted cash flow \| Power purchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets \| $	33	31
Liabilities \| $	$ 89	$ 47
CRR auction prices \| Market approach \| Congestion revenue rights \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (in dollars per mwh)	(74)	(74)
CRR auction prices \| Market approach \| Congestion revenue rights \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (in dollars per mwh)	74	74
CRR auction prices \| Market approach \| Congestion revenue rights \| Weighted average price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (in dollars per mwh)	2	2
Forward prices \| Discounted cash flow \| Power purchase agreements \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (in dollars per mwh)	13	11
Forward prices \| Discounted cash flow \| Power purchase agreements \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (in dollars per mwh)	96	106
Forward prices \| Discounted cash flow \| Power purchase agreements \| Weighted average price
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range (in dollars per mwh)	47	53