FAIR VALUE MEASUREMENTS AND DERIVATIVE INSTRUMENTS (Derivative Volumes) (Details) BTU in Billions	12 Months Ended
	Dec. 31, 2021 BTU GWh	Dec. 31, 2020 BTU GWh
Power Contracts GWh
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, nonmonetary notional amount | GWh	2,617	4,143
Gas Contracts BBtu
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, nonmonetary notional amount | BTU	112,316	111,585