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INVESTMENT IN TRANSMISSION AFFILIATES - RELATED PARTY TRANSACTIONS (Details) - ATC - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2026 | Jun. 30, 2025 | Jun. 30, 2026 | Jun. 30, 2025
Investment in transmission affiliates |  |  |  |
Charges to ATC for services and construction | $ 6.1 | $ 5.0 | $ 13.4 | $ 9.5
Charges from ATC for network transmission services | 129.0 | 116.7 | 258.2 | 233.4
Net refund (payment) from (to) ATC related to FERC ROE orders | $ (0.7) | $ 0.3 | $ 1.3 | $ 1.7

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