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DERIVATIVE INSTRUMENTS - GAINS (LOSSES) AND NOTIONAL VOLUMES (Details) MWh in Millions, MMBTU in Millions, $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2025 USD ($) MMBTU MWh | Sep. 30, 2024 USD ($) MWh MMBTU | Sep. 30, 2025 USD ($) MMBTU MWh | Sep. 30, 2024 USD ($) MWh MMBTU
Realized gains and losses |  |  |  |
Gains (losses) | $ (7.0) | $ (20.0) | $ 2.4 | $ (103.1)
Natural gas contracts |  |  |  |
Realized gains and losses |  |  |  |
Gains (losses) | $ (13.6) | $ (24.0) | $ (9.0) | $ (110.7)
Notional sales volumes |  |  |  |
Notional sales volumes | MMBTU | 37.6 | 38.6 | 146.4 | 154.5
FTRs and TCRs |  |  |  |
Realized gains and losses |  |  |  |
Gains (losses) | $ 6.6 | $ 4.0 | $ 11.4 | $ 7.6
Notional sales volumes |  |  |  |
Notional sales volumes | MWh | 6.8 | 7.9 | 21.2 | 23.1

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