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Pension and Other Post-retirement Benefits Net Periodic Pension Costs and Weighted Average Assumptions (Details) - USD ($)
$ in Millions
 4 Months Ended 8 Months Ended 9 Months Ended 12 Months Ended
Apr. 30, 2021
Apr. 30, 2021
Dec. 31, 2021
Dec. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]            
Service cost   $ 0.0 $ 0.0 $ 1.5 $ 0.1  
Interest cost   6.6 15.6 21.3 25.4  
Expected return on plan assets   (12.1) (24.7) (27.1) (36.5)  
Curtailment gain recognized (2)   0.0 0.0 0.0 (3.3)  
Settlement (gain) loss recognized (2)   0.0 0.4 0.0 (0.3)  
Defined Benefit Plan, Amortization of Gain (Loss)   0.1 0.0 0.0 0.0  
Net periodic pension costs   $ (5.4) $ (8.7) $ (4.3) $ (14.6) $ (4.3)
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets 6.03% 6.03% 6.03% 6.70% 6.48%  
Cash balance interest credit rate   2.94% 2.94% 3.29% 3.29%  
Pension Benefits            
Defined Benefit Plan Disclosure [Line Items]            
Service cost   $ 0.0 $ 0.0   $ 0.1  
Interest cost   6.5 15.3   24.9  
Curtailment gain recognized (2)   $ 0.0 $ 0.0   $ (3.3)  
Discount rate   2.30% 2.84% 3.82% 3.16%