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Changes in Accumulated Other Comprehensive Loss (Details of Accumulated Other Comprehensive Income Components) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Amortization of pension and postretirement components $ 2.1 $ 0.6
Total before tax 28.1 46.7
Tax impact 6.4 8.9
Net income attributable to common shareholders 21.7 37.8
Reclassification out of Accumulated Other Comprehensive Income | Pension and Postretirement Benefits    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Total before tax (0.3) (0.5)
Tax impact (0.1) (0.1)
Net income attributable to common shareholders (0.2) (0.4)
Pension Plan [Member] | Reclassification out of Accumulated Other Comprehensive Income | Prior service costs    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Amortization of pension and postretirement components (0.2) (0.2)
Pension Plan [Member] | Reclassification out of Accumulated Other Comprehensive Income | Net gain (loss)    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Amortization of pension and postretirement components 0.0 0.1
Postretirement | Reclassification out of Accumulated Other Comprehensive Income | Prior service costs    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Amortization of pension and postretirement components 0.0 (0.2)
Postretirement | Reclassification out of Accumulated Other Comprehensive Income | Net gain (loss)    
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]    
Amortization of pension and postretirement components $ (0.1) $ (0.2)