Summary of Activity for Valuation Allowances (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning balance, Accounts receivable allowance	$ (25.7)	$ (27.5)	$ (29.4)
Charged to costs and expenses, Accounts receivable allowance	(19.6)	(6.2)	(9.0)
Deductions, Accounts receivable allowance	8.7	8.0	10.9
Ending balance, Accounts receivable allowance	(36.6)	(25.7)	(27.5)
Beginning balance, Deferred tax assets valuation allowance	(3.2)	(4.3)	(6.9)
Charged to costs and expenses, Deferred Tax Allownces	(9.9)	(0.9)	2.4
Deductions, Deferred tax assets valuation allowance	0.3	2.0	0.2
Ending balance, Deferred tax assets valuation allowance	$ (12.8)	$ (3.2)	$ (4.3)