Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning Balance	$ 7.1	$ 4.1	$ 4.3
Charge to Expenses	1.1	4.0	0.5
Charged (credited) to other accounts	0.4	(0.4)	(0.3)
Deductions	(4.4)	(0.6)	(0.4)
Balance at end of period	4.2	7.1	4.1
Tax Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning Balance	149.8	137.0	144.1
Additions Charged to Income	25.8	9.1	11.6
Additions Charged to Equity	13.8	3.7	(18.7)
Deductions	0.0	0.0	0.0
Balance at end of period	$ 189.4	$ 149.8	$ 137.0