Other Comprehensive (Loss) Income - Schedule of Components of Other Comprehensive (Loss) Income and Income Tax Expense (Benefit) Allocated to Each Component (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive loss, Before Tax Amount	$ (6.3)	$ 17.1	$ (23.2)	$ (72.3)
Other comprehensive loss, Income Tax	0.5	0.5	2.0	(1.9)
Other comprehensive (loss) income	(6.8)	16.6	(25.2)	(70.4)
Translation adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive loss, Before Tax Amount	(8.4)	17.7	(31.1)	46.8
Other comprehensive loss, Income Tax	0.0		0.0
Other comprehensive (loss) income	(8.4)	17.7	(31.1)	46.8
Adjustment for net periodic pension and OPEB cost
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive loss, Before Tax Amount	2.1	1.2	7.9	3.2
Other comprehensive loss, Income Tax	0.5	0.5	2.0	1.1
Other comprehensive (loss) income	$ 1.6	0.7	$ 5.9	2.1
Adjustments for available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive loss, Before Tax Amount		(1.8)		(122.3)
Other comprehensive loss, Income Tax				(3.0)
Other comprehensive (loss) income		$ (1.8)		$ (119.3)