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Pension and Other Postretirement Benefits - Change in Plan Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Pension    
Change in fair value of plan assets [Roll Forward]    
Fair value of plan assets at beginning of year $ 329.7 $ 318.8
Actual return on plan assets (93.3) 30.3
Employer contributions 4.2 1.8
Medicare Part D subsidy received 0.0 0.0
Benefits paid (24.0) (21.2)
Fair value of assets at end of year 216.6 329.7
OPEB    
Change in fair value of plan assets [Roll Forward]    
Fair value of plan assets at beginning of year 0.0 0.0
Actual return on plan assets 0.0 0.0
Employer contributions 5.9 5.9
Medicare Part D subsidy received 0.2 0.2
Benefits paid (6.1) (6.1)
Fair value of assets at end of year $ 0.0 $ 0.0