Discontinued Operations - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss (Income) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ (1.5)	$ 4.2	$ 39.4
Unrecognized Tax Benefits, Interest on Income Taxes Expense	$ 2.4	$ 2.9	5.7
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Tax Matters Agreement Receivable, Discontinued Operations			13.2
Recognition of Previously Unrecognized Tax Position [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Tax Adjustments, Settlements, and Unusual Provisions			(38.3)
Unrecognized Tax Benefits, Interest on Income Taxes Expense			(3.2)
Tax Expense from Audit Adjustments [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Tax Adjustments, Settlements, and Unusual Provisions			$ (17.4)