INVESTMENT IN TRANSMISSION AFFILIATES - RELATED PARTY TRANSACTIONS (Details) - ATC - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Investment in transmission affiliates
Charges to ATC for services and construction	$ 4.5	$ 4.5	$ 15.5	$ 12.3
Charges from ATC for network transmission services	$ 103.4	$ 94.3	$ 309.9	$ 283.1