Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2021	Sep. 07, 2021	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Net loss	$ (27.2)	$ (81.3)	$ (192.7)	$ (130.9)
Other comprehensive income (loss), net of tax:
Foreign currency translation gain (loss)	(1.4)	1.2	2.6	(6.2)
Cash flow hedges:
Unrealized loss on cash flow hedges arising during the period, net of tax of $0.0	0.0	(0.1)	0.0	0.0
Reclassification adjustment for net losses included in net income, net of tax of $5.8	0.0	19.7	0.0	0.0
Defined benefit plans:
Net gain arising from remeasurement during the period, net of tax of $0.7, $7.8, $0.8, $1.8	2.6	6.0	10.5	25.1
Amortization of prior service benefits included in net income, net of tax of ($0.2), ($0.4)	0.0	(1.3)	(0.6)	0.0
Amortization of net actuarial (gain) loss included in net income, net of tax of ($1.2), ($0.2), $3.6	0.0	12.0	(3.8)	(0.6)
Total other comprehensive income, net of tax	1.2	37.5	8.7	18.3
Total comprehensive loss	$ (26.0)	$ (43.8)	$ (184.0)	$ (112.6)