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Reclassifications out of Accumulated Other Comprehensive Loss - Summary of Reclassifications out of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Liquidation of subsidiary	$ 0.0	$ 0.0	$ 1.8	$ 0.0
Total reclassifications			(2.5)
Foreign Currency Translation Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications			0.0
Defined Benefit Pension Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications			(2.5)
Reclassification Out of Accumulated Other Comprehensive Income/(Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax			4.8
Income tax expense			(0.5)
Total reclassifications			4.3
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			(0.7)
Amortization of actuarial net losses			$ 3.7