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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

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