Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (8.2)	$ (13.6)	$ (50.0)	$ (46.0)
Other comprehensive income (loss), net of tax:
Foreign currency translation gain (loss)	2.0	(1.0)	(2.1)	2.1
Cash flow hedges:
Unrealized loss on cash flow hedges arising during the period, net of tax of ($0.1), $(0.9), ($3.3), ($4.2)	(0.5)	(3.0)	(11.3)	(13.9)
Reclassification adjustment for net losses included in net income, net of tax of $0.5, $0.2, $1.4, $0.3	1.8	0.4	4.6	0.8
Defined benefit plans:
Net gain (loss) arising from remeasurement during the period, net of tax of $1.0, ($3.4), $0.0	3.2	0.0	(11.5)	0.1
Amortization of prior service benefits included in net income, net of tax of ($0.1), ($0.2), ($0.4), ($0.5)	(0.5)	(0.4)	(1.5)	(1.4)
Amortization of net actuarial loss included in net income, net of tax of $1.1, $1.0, $3.3, $2.7	3.7	2.9	11.1	8.9
Reclassification adjustment for pension settlement charges included in net income, net of tax of $0.2	0.0	0.0	0.9	0.0
Total other comprehensive income (loss)	9.7	(1.1)	(9.8)	(3.4)
Total comprehensive income (loss)	$ 1.5	$ (14.7)	$ (59.8)	$ (49.4)