Other Comprehensive (Loss) Income - Schedule of Changes in Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ (370.3)	$ (245.4)
Amounts reclassified from accumulated other comprehensive (loss) income	0.6	(4.7)
Other comprehensive (loss) income	(31.2)	1.6
Ending Balance	(416.6)	(250.0)
Changes in Fair Value of Derivatives
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	1.0
Other comprehensive (loss) income before reclassifications	(11.8)
Amounts reclassified from accumulated other comprehensive (loss) income	(0.2)
Other comprehensive (loss) income	(12.0)
Ending Balance	(11.0)
Pension and OPEB Cost
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(185.7)	(155.2)
Amounts reclassified from accumulated other comprehensive (loss) income	0.8	(0.2)
Other comprehensive (loss) income	0.8	(0.2)
Ending Balance	(184.9)	(155.4)
Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	8.5	1.4
Other comprehensive (loss) income before reclassifications	(19.8)	5.5
Amounts reclassified from accumulated other comprehensive (loss) income		(4.5)
Other comprehensive (loss) income	(19.8)	1.0
Ending Balance	(11.3)	2.4
Other
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income before reclassifications		0.6
Other comprehensive (loss) income		0.6
Ending Balance		0.6
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(176.2)	(153.8)
Other comprehensive (loss) income before reclassifications	(31.6)	6.1
Amounts reclassified from accumulated other comprehensive (loss) income	0.6	(4.7)
Other comprehensive (loss) income	(31.0)	1.4
Ending Balance	$ (207.2)	$ (152.4)