INVESTMENT IN TRANSMISSION AFFILIATES - RELATED PARTY TRANSACTIONS (Details) - ATC - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Investment in transmission affiliates
Charges to ATC for services and construction	$ 4.0	$ 4.7	$ 7.8	$ 10.9
Charges from ATC for network transmission services	$ 94.3	$ 90.8	$ 188.8	$ 181.9