INVESTMENT IN TRANSMISSION AFFILIATES - RELATED PARTY TRANSACTIONS (Details) - ATC - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Investment in transmission affiliates
Charges to ATC for services and construction	$ 6.3	$ 4.0	$ 11.0	$ 7.8
Charges from ATC for network transmission services	$ 103.2	$ 94.3	$ 206.5	$ 188.8