DERIVATIVE INSTRUMENTS - GAINS (LOSSES) AND NOTIONAL VOLUMES (Details) MWh in Millions, MMBTU in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) MWh MMBTU	Sep. 30, 2021 USD ($) MMBTU MWh	Sep. 30, 2022 USD ($) MMBTU MWh	Sep. 30, 2021 USD ($) MMBTU MWh
Realized gains
Gains	$ 126.5	$ 44.2	$ 272.3	$ 53.8
Natural gas contracts
Notional sales volumes
Notional sales volumes | MMBTU	32.7	39.4	133.3	147.1
Realized gains
Gains	$ 119.1	$ 41.2	$ 259.6	$ 38.5
FTRs and TCRs
Notional sales volumes
Notional sales volumes | MWh	7.0	6.3	21.0	22.1
Realized gains
Gains	$ 7.4	$ 3.0	$ 12.7	$ 15.3