Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net loss	$ (61.4)	$ (42.7)	$ (136.6)	$ (122.7)
Other comprehensive income (loss), net of tax:
Foreign currency translation gain (loss)	1.3	(1.8)	(2.3)	0.6
Defined benefit plans:
Net gain arising from remeasurement during the period, net of tax of $2.2, $1.3	6.7	0.0	3.9	0.0
Amortization of prior service benefits included in net income, net of tax of ($0.1), ($0.1), ($0.2), ($0.2)	(0.1)	(0.1)	(0.4)	(0.4)
Amortization of net actuarial gain included in net income, net of tax of ($0.2), ($0.2), ($0.7), ($0.8)	(0.8)	(1.1)	(2.3)	(2.9)
Reclassification adjustment for pension settlement benefits included in net income, net of tax of ($0.6), ($0.7)	(2.2)	0.0	(2.5)	0.0
Total other comprehensive income (loss)	4.9	(3.0)	(3.6)	(2.7)
Total comprehensive loss	$ (56.5)	$ (45.7)	$ (140.2)	$ (125.4)