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Components of Net Periodic Pension Cost (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Apr. 01, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Predecessor | Pension Plans, Defined Benefit [Member]        
Components of net periodic pension costs        
Service cost for benefits earned $ 0.6   $ 2.5 $ 2.7
Interest cost on projected benefit obligation 9.7   41.5 40.4
Expected return on plan assets (11.0)   (45.3) (48.2)
Amortization of prior service cost 0.1   0.3 1.0
Amortization of actuarial losses 6.3   24.7 39.6
Settlement charge 0.0   0.0 0.0
Net actuarial gain 0.0   0.0 0.0
Net periodic pension cost $ 5.7   $ 23.7 $ 35.5
Successor        
Components of net periodic pension costs        
Service cost for benefits earned   $ 6.9    
Interest cost on projected benefit obligation   24.2    
Successor | Pension Plans, Defined Benefit [Member]        
Components of net periodic pension costs        
Service cost for benefits earned   1.6    
Interest cost on projected benefit obligation   28.0    
Expected return on plan assets   (33.5)    
Amortization of prior service cost   0.0    
Amortization of actuarial losses   0.0    
Settlement charge   (2.1)    
Net actuarial gain   (23.5)    
Net periodic pension cost   $ (25.3)