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Employee Benefit Plans (Net Periodic Pension Costs Included in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
After-Tax Amount      
Prior service (cost) credit arising during the year $ (19.1) $ 10.0 $ 0.3
Net (gain) loss recognized due to settlement (0.4) 0.1 0.3
Net loss recognized due to curtailment 0.0 6.3 0.0
Net actuarial gain arising during the year 12.3 53.6 (32.7)
Amortization of prior service cost 0.0 0.6 2.1
Amortization of net actuarial losses 6.4 12.3 13.1
Defined Benefit Pension Plans      
After-Tax Amount      
Prior service (cost) credit arising during the year (19.1) 10.0 0.3
Net (gain) loss recognized due to settlement (0.4) 0.1 0.3
Net loss recognized due to curtailment   6.3  
Net actuarial gain arising during the year 12.3 53.6 (32.7)
Amortization of prior service cost   0.6 2.1
Amortization of net actuarial losses 6.4 12.3 13.1
Postretirement benefits      
Before-Tax Amount      
Accumulated other comprehensive loss, beginning of period (2.1)    
Accumulated other comprehensive loss, end of period (1.1) (2.1)  
Net prior service cost 3.1 3.2  
Postretirement benefits | Defined Benefit Pension Plans      
Before-Tax Amount      
Accumulated other comprehensive loss, beginning of period (302.4) (412.5)  
Prior service credit arising during the year (25.5) 13.1  
Net loss recognized due to settlement (0.4) 0.1  
Net loss recognized due to curtailment   8.5  
Net actuarial gain arising during the year 15.0 71.0  
Amortization of prior service cost 0.2 0.8  
Amortization of net actuarial losses 8.7 16.6  
Accumulated other comprehensive loss, end of period (304.4) (302.4) (412.5)
Income Tax      
Accumulated other comprehensive loss, beginning of period (72.0) (99.2)  
Prior service credit arising during the year (6.4) 3.1  
Net loss recognized due to settlement 0.0 0.0  
Net loss recognized due to curtailment   2.2  
Net actuarial gain arising during the year 2.7 17.4  
Amortization of prior service cost 0.2 0.2  
Amortization of net actuarial losses 2.3 4.3  
Accumulated other comprehensive loss, end of period (73.2) (72.0) (99.2)
After-Tax Amount      
Accumulated other comprehensive loss, , beginning of period (230.4) (313.3)  
Prior service (cost) credit arising during the year (19.1) 10.0  
Net (gain) loss recognized due to settlement (0.4) 0.1  
Net loss recognized due to curtailment   6.3  
Net actuarial gain arising during the year 12.3 53.6  
Amortization of prior service cost 0.0 0.6  
Amortization of net actuarial losses 6.4 12.3  
Accumulated other comprehensive loss, end of period $ (231.2) $ (230.4) $ (313.3)