Business Acquisitions (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 1,089.0	$ 991.0	$ 928.5
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Tangible assets acquired	34.4
Intangible assets	63.6
Goodwill	88.5
Net deferred taxes	(0.2)
Other liabilities assumed	(14.8)
TOTAL CONSIDERATION, NET OF CASH RECEIVED	$ 171.5