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Pension and Other Postretirement Benefit Plans - Obligation and Funded Status (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Change in Plan Assets      
Non-Current Liabilities $ (160.8) $ (179.7)  
Pension      
Defined Benefit Plan Disclosure [Line Items]      
Accumulated Benefit Obligation 729.5 724.5  
Change in Benefit Obligation [Roll Forward]      
Obligation, Beginning of Year 739.7 911.7  
Service Cost 6.5 9.3 $ 11.0
Interest Cost 40.5 27.2 24.6
Plan Amendments 0.0 0.8  
Actuarial (Gain) Loss 13.9 (160.6)  
Benefits Paid (60.9) (58.9)  
Participant Contributions 6.6 10.2  
Obligation, End of Year 746.3 739.7 911.7
Change in Plan Assets      
Fair Value, Beginning of Year 568.6 745.7  
Actual Return on Plan Assets 55.1 (130.5)  
Employer contribution 26.2 12.3  
Benefits Paid (60.9) (58.9)  
Fair Value, End of Year 589.0 568.6 745.7
Funded Status, End of Year (157.3) (171.1)  
Current Liabilities (2.1) (2.1)  
Non-Current Liabilities (155.2) (169.0)  
Postretirement Health and Life Obligation and Funded Status      
Change in Benefit Obligation [Roll Forward]      
Obligation, Beginning of Year 110.4 148.2  
Service Cost 2.0 3.0 3.6
Interest Cost 5.6 4.4 4.4
Plan Amendments (29.1) 0.0  
Actuarial (Gain) Loss (9.3) (38.7)  
Benefits Paid (8.1) (9.2)  
Participant Contributions 2.4 2.7  
Obligation, End of Year 73.9 110.4 148.2
Change in Plan Assets      
Fair Value, Beginning of Year 162.6 201.8  
Actual Return on Plan Assets 20.3 (33.0)  
Employer Contribution (Withdrawal) (3.4)    
Employer contribution   0.3  
Benefits Paid (8.1) (9.2)  
Participant Contributions 2.4 2.7  
Fair Value, End of Year 173.8 162.6 $ 201.8
Funded Status, End of Year 99.9 52.2  
Non-Current Assets 106.3 58.8  
Current Liabilities (0.2) (0.2)  
Non-Current Liabilities $ (6.2) $ (6.4)