Income Taxes - Reconciliations of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 71.1	$ 45.6	$ 40.3
Gross increases for tax positions in prior periods	5.3	27.4	4.7
Gross decreases for tax positions in prior periods	(5.0)	4.8	1.5
Gross increases based on tax positions related to the current year	1.8	2.0	1.3
Gross decreases related to settlements with taxing authorities	(35.7)	3.4	1.9
Reductions due to statute expiration	(2.2)	0.8	1.4
Unrecognized Tax Benefits, Increase Resulting from Foreign Currency Translation	(1.3)	(0.2)	(2.5)
Gross increases due to acquisitions	0.0	5.3	6.6
Ending balance	$ 36.6	$ 71.1	$ 45.6