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Accumulated Other Comprehensive Income (Loss) - Schedule of Components of Accumulated Other Comprehensive Income (Loss), Net of Taxes (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance $ 1,035.7 $ 1,066.6 $ 1,096.1
Other comprehensive income (loss) before reclassifications, net of taxes 0.4 21.9 (25.1)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes of 1.0 78.9 4.4
Income taxes related to other comprehensive income (loss) 0.0 (18.3) 0.0
Ending balance 1,003.0 1,035.7 1,066.6
Other comprehensive income (loss) before reclassifications, tax 0.0 0.0 0.0
Amounts reclassified from accumulated other comprehensive loss, tax 0.0 0.0 0.0
Other Post-retirement Benefits      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Income taxes related to other comprehensive income (loss) 0.0 (0.1) 0.0
Non-qualified benefit plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Income taxes related to other comprehensive income (loss) 0.0 0.1 0.0
Accumulated Other Comprehensive Income (Loss)      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance 1.8 (80.7) (60.0)
Ending balance 3.2 1.8 (80.7)
Employee Benefit Plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance (0.3) (77.9) (53.3)
Other comprehensive income (loss) before reclassifications, net of taxes 0.1 17.0 (27.4)
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes of 0.0 78.9 2.8
Income taxes related to other comprehensive income (loss)   (18.3)  
Ending balance (0.2) (0.3) (77.9)
Employee Benefit Plans | Qualified Plans | Other Post-retirement Benefits      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance (0.3)    
Ending balance (0.2) (0.3)  
Employee Benefit Plans | Non-qualified Plan Benefits | Non-qualified benefit plans      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance 0.0    
Ending balance 0.0 0.0  
Interest Rate Swap      
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]      
Beginning balance 2.1 (2.8) (6.7)
Other comprehensive income (loss) before reclassifications, net of taxes 0.3 4.9 2.3
Amounts reclassified from accumulated other comprehensive income (loss), net of taxes of 1.0 0.0 1.6
Income taxes related to other comprehensive income (loss)   0.0  
Ending balance $ 3.4 $ 2.1 $ (2.8)