Pension and Savings Plans Pre-tax Amounts Recorded to Accumulated Other Comprehensive Loss (Details) - Pension Plan - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Apr. 01, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Successor
Amortization:
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		$ 23.5	$ (4.2)
Predecessor
Amounts recognized in accumulated other comprehensive loss
Net actuarial loss arising during period	$ 0.0			$ 6.6
Amortization:
Net actuarial loss	6.3			24.7
Prior service cost	(0.1)			(0.3)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	0.0			0.0
Total recorded in “Accumulated other comprehensive income”	$ (6.4)			$ (18.4)