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FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Schedule of Derivative Volumes) (Details)
GWh in Thousands, BTU in Billions
9 Months Ended 12 Months Ended
Sep. 30, 2026
GWh
BTU
Dec. 31, 2025
GWh
BTU
Power Contracts GWh    
Derivative Volume [Line Items]    
Derivative, energy measure | GWh 5,283 1,430
Gas Contracts BBtu    
Derivative Volume [Line Items]    
Derivative, energy measure | BTU 63,845 72,959