Other Comprehensive (Loss) Income - Schedule of Components of Other Comprehensive (Loss) Income and Income Tax Expense Allocated to Each Component (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, Before Tax Amount	$ (42.8)	$ 104.2	$ 4.6
Other comprehensive (loss) income, Income Tax Expense	4.5	12.0	25.4
Other comprehensive (loss) income	(47.3)	92.2	(20.8)
Translation adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, Before Tax Amount	57.1	(38.3)	(55.7)
Other comprehensive (loss) income	57.1	(38.3)	(55.7)
Adjustment for net periodic pension and other postretirement benefits plan cost
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, Before Tax Amount	22.4	20.2	60.2
Other comprehensive (loss) income, Income Tax Expense	7.5	9.0	25.4
Other comprehensive (loss) income	14.9	11.2	34.8
Adjustment for available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, Before Tax Amount	(122.3)	122.3
Other comprehensive (loss) income, Income Tax Expense	(3.0)	3.0
Other comprehensive (loss) income	$ (119.3)	$ 119.3
Change in fair value of derivatives
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, Before Tax Amount			0.1
Other comprehensive (loss) income			$ 0.1