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INVESTMENT IN TRANSMISSION AFFILIATES - RELATED PARTY TRANSACTIONS (Details) - ATC - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Investment in transmission affiliates        
Charges to ATC for services and construction $ 4.2 $ 4.5 $ 13.7 $ 15.5
Charges from ATC for network transmission services 116.8 103.4 350.2 309.9
Refund from ATC related to FERC ROE orders $ 2.1 $ 0.0 $ 3.8 $ 0.0