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Significant Accounting Policies (Gain on Asset Dispositions) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Property, Plant and Equipment [Abstract] |  |  |
Disposition gains | $ 122.0 | $ 119.8 | $ 104.1
Residual sharing income | (0.5) | (0.9) | (5.6)
Non-remarketing disposition gains | (15.8) | (11.1) | (17.1)
Asset impairments | 0.0 | (1.5) | (48.9)
Net gain on asset dispositions | $ 138.3 | $ 130.3 | $ 77.9

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