Other Comprehensive (Loss) Income - Schedule of Components of Other Comprehensive Income (Loss) and Income Tax (Benefit) Expense Allocated to Each Component (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, Before Tax Amount	$ 17.1	$ (36.8)	$ (72.3)	$ (25.3)
Other comprehensive (loss) income, Income Tax Expense	0.5	(13.0)	(1.9)	(3.0)
Other comprehensive income (loss)	16.6	(23.8)	(70.4)	(22.3)
Translation adjustments
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, Before Tax Amount	17.7	(4.4)	46.8	(9.0)
Other comprehensive (loss) income, Income Tax Expense	0.0	0.0	0.0	0.0
Other comprehensive income (loss)	17.7	(4.4)	46.8	(9.0)
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	1.2	(32.4)	3.2	(16.3)
Other comprehensive (loss) income, Income Tax Expense	0.5	(13.0)	1.1	(3.0)
Other comprehensive income (loss)	0.7	$ (19.4)	2.1	$ (13.3)
Adjustments for available-for-sale securities
Accumulated Other Comprehensive Income Loss [Line Items]
Other comprehensive (loss) income, Before Tax Amount	(1.8)		(122.3)
Other comprehensive (loss) income, Income Tax Expense	0.0		(3.0)
Other comprehensive income (loss)	$ (1.8)		$ (119.3)