Income Taxes - Components of Income Taxes and Comprehensive Provision for Income Taxes Allocation (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule Of Income Tax [Line Items]
Expected tax expense, at U.S. federal statutory income tax rate of 35% in 2017 and 21% in 2018	$ 9.8		$ 28.0	$ 53.9	$ 67.6
Non-U.S. tax rates	3.6		(3.4)	18.6	(8.2)
Incremental net tax expense on earnings and losses of U.S. and non-U.S. companies	1.8		0.2	2.9	6.8
Valuation allowance			(7.8)		(170.4)
Adjustment to reserve for uncertain tax positions, net			(8.1)	1.4	(7.6)
Transition tax	(1.7)	$ 76.2		(1.7)
Other, net	0.6		0.4	1.8	1.0
Income tax expense (benefit)	14.1		6.1	75.5	(114.0)
Comprehensive provision for income taxes (benefit) allocable to:
Net income	14.1		6.1	75.5	(114.0)
Other comprehensive income (loss):
Currency translation			6.4		19.7
Marketable securities			(0.3)		(0.6)
Interest rate swap			1.0		1.1
Total	15.1		14.3	78.6	(90.7)
Canada - Germany APA
Schedule Of Income Tax [Line Items]
Canada-Germany APA			(3.2)	(1.4)	(3.2)
Defined Benefit Pension Plans
Other comprehensive income (loss):
Benefit plans	$ 1.0		$ 1.1	3.2	3.2
OPEB
Other comprehensive income (loss):
Benefit plans				$ (0.1)	$ (0.1)