Acquisitions and Dispositions - Schedule of Purchase Price Allocation for Acquisitions (Detail) - USD ($) $ in Millions		12 Months Ended
	Aug. 04, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill		$ 602.0	$ 1,085.7	$ 588.5
Net cash paid		$ 48.1	$ 118.2
Precision Dialogue Holdings, LLC
Business Acquisition [Line Items]
Accounts receivable	$ 11.5
Inventories	0.4
Prepaid expenses and other current assets	0.8
Property, plant and equipment	6.9
Other intangible assets	14.1
Other noncurrent assets	1.2
Goodwill	42.5
Accounts payable and accrued liabilities	(11.4)
Deferred taxes-net	(6.8)
Total purchase price-net of cash acquired	59.2
Less: debt assumed	11.1
Net cash paid	$ 48.1