Schedule of Payments for Acquisitions of Businesses and Interests in Affiliates, Net of Cash Acquired (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Fair value of assets acquired, excluding cash	$ (17.2)	$ (529.5)	$ (146.4)
Liabilities assumed	0.3	50.9	7.9
Fair value of earn-out and deferred purchase consideration	3.1		39.6
Less: Non-controlling interest		252.3
Payments to acquire businesses, net of cash acquired	(13.8)	(226.3)	(98.9)
Payments to acquire equity method investments	(111.5)
Payments to acquire additional interests in subsidiaries			(4.2)
Payments to acquire businesses and interests in affiliates, total	$ (125.3)	$ (226.3)	$ (103.1)