Accumulated Other Comprehensive Loss - Summary of Reclassifications Out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	$ 17.9	$ 10.6
Tax benefit	(7.7)	(2.8)
Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	0.5	1.6
Tax benefit	0.0	(0.6)
Net income (loss)	0.5	1.0
Amount Reclassified from Accumulated Other Comprehensive Loss | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial losses	0.2	1.6
Amount Reclassified from Accumulated Other Comprehensive Loss | Curtailment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial losses	$ 0.3	$ 0.0