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Pension and Other Postretirement Benefits - Pension Plan Assets Fair Value (Details) - Pensions - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets $ 963.0 $ 1,041.3 $ 1,044.1
Quoted Prices in Active Markets for Identical Assets (Level 1)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 196.0 220.7  
Significant Other Observable Inputs (Level 2)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 767.0 820.6  
Significant Unobservable Inputs (Level 3)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
Cash and short-term investments      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 43.5 3.0  
Cash and short-term investments | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 43.5 3.0  
Cash and short-term investments | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
Cash and short-term investments | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
Investment contracts      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 108.6 114.9  
Investment contracts | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
Investment contracts | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 108.6 114.9  
Investment contracts | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
U.S. Government Securities      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 138.8 204.6  
U.S. Government Securities | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 138.8 204.6  
U.S. Government Securities | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
U.S. Government Securities | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
Mutual funds      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 13.7 13.1  
Mutual funds | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 13.7 13.1  
Mutual funds | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
Mutual funds | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
Corporate debt instruments      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 658.4 705.7  
Corporate debt instruments | Quoted Prices in Active Markets for Identical Assets (Level 1)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 0.0 0.0  
Corporate debt instruments | Significant Other Observable Inputs (Level 2)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets 658.4 705.7  
Corporate debt instruments | Significant Unobservable Inputs (Level 3)      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Fair value of plan assets $ 0.0 $ 0.0