Other Comprehensive Loss - Schedule of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ (243.8)	$ (370.3)
Amounts reclassified from accumulated other comprehensive loss	2.4	0.6
Other comprehensive loss	(6.6)	(31.2)
Ending Balance	(254.4)	(416.6)
Changes in Fair Value of Derivatives
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(11.0)	1.0
Other comprehensive income (loss) before reclassifications	1.2	(11.8)
Amounts reclassified from accumulated other comprehensive loss	1.3	(0.2)
Other comprehensive loss	2.5	(12.0)
Ending Balance	(8.5)	(11.0)
Pension and OPEB Cost
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(178.5)	(185.7)
Amounts reclassified from accumulated other comprehensive loss	1.1	0.8
Other comprehensive loss	1.1	0.8
Ending Balance	(177.4)	(184.9)
Translation Adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	35.6	8.5
Other comprehensive income (loss) before reclassifications	(10.0)	(19.8)
Other comprehensive loss	(10.0)	(19.8)
Ending Balance	25.6	(11.3)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(153.9)	(176.2)
Other comprehensive income (loss) before reclassifications	(8.8)	(31.6)
Amounts reclassified from accumulated other comprehensive loss	2.4	0.6
Other comprehensive loss	(6.4)	(31.0)
Ending Balance	$ (160.3)	$ (207.2)