Valuation and Qualifying Accounts - Allowance for Uncollectible Accounts Receivable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 55.7	$ 54.2	$ 59.5
Charges to costs and expenses	9.5	16.7	11.4
Deductions:
Dispositions	(1.0)	(2.5)	(2.8)
Uncollectible accounts written off	(25.5)	(9.4)	(9.8)
Foreign currency translation adjustment	4.0	(3.3)	(4.1)
Balance at end of period	$ 42.7	$ 55.7	$ 54.2