Reclassifications out of Accumulated Other Comprehensive Loss - Summary of Reclassifications out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Liquidation of subsidiary	$ 1.8	$ 0.0	$ 0.0
Total reclassifications	(3.3)
Total reclassifications	(3.3)
Foreign Currency Translation Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications	0.0
Total reclassifications	0.0
Defined Benefit Pension Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications	(3.3)
Total reclassifications	(3.3)
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	4.0
Income tax expense	(0.7)
Total reclassifications	5.1
Total reclassifications	5.1
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member] | Foreign Currency Translation Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Liquidation of subsidiary	1.8
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member] | Defined Benefit Pension Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service credit	(1.0)
Amortization of actuarial net losses	$ 5.0