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Retirement Plans - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2024
Sep. 30, 2023
Sep. 30, 2024
Sep. 30, 2023
Defined Benefit Pension Plan        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 4.2 $ 3.9 $ 12.3 $ 11.6
Interest cost 4.8 5.3 14.4 15.8
Expected return on assets (4.8) (4.8) (14.1) (14.2)
Curtailments 0.0 0.0 (1.3) 0.0
Net gain (0.3) (0.8) (1.1) (2.5)
Prior service credit 0.2 0.2 0.5 0.5
Total benefit cost 4.1 3.8 10.7 11.2
Retiree Health Care Plan        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 0.1 0.1 0.3 0.4
Prior service credit (0.2) (0.2) (0.6) (0.6)
Total benefit cost $ (0.1) $ (0.1) $ (0.3) $ (0.2)