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Selected Balance Sheet Information: Materials, Supplies, and Fuel Schedule (Details) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
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Selected Balance Sheet Information [Abstract] |  |
Materials and supplies | $ 114.1 | $ 106.1
Fuel - Electric Utilities | 6.7 | 7.5
Natural gas in storage | 52.2 | 40.3
Total materials, supplies and fuel | $ 173.0 | $ 153.9

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