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Pension and Postretirement Benefit Plans (Net Pension And Postretirement Cost) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Pension plan      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 9.6 $ 12.8 $ 15.0
Interest cost 29.3 14.8 12.6
Expected return on plan assets (30.4) (16.9) (31.3)
Amortization of net actuarial losses 9.4 8.7 16.5
Amortization of prior service cost 1.5 0.1 0.7
Net (gain) loss recognized due to settlement 0.4 (0.4) 0.1
Curtailment gain 0.0 0.0 (1.2)
Net annual postretirement benefit cost $ 19.8 $ 19.1 $ 12.4
Weighted average discount rate 4.90% 1.90% 1.50%
Postretirement benefits      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 0.1 $ 0.1 $ 0.1
Interest cost 1.3 0.9 0.9
Amortization of net actuarial losses 0.0 0.0 0.1
Amortization of prior service cost 0.2 0.1 0.1
Net annual postretirement benefit cost $ 1.6 $ 1.1 $ 1.2
Weighted average discount rate 6.60% 4.10% 3.80%