Schedule II - Valuation and Qualifying Accounts (Details) - Allowance for Doubtful Accounts - 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 Year	$ 3.5	$ 3.6	$ 4.7
Charged to Expense / Against Revenue	3.7	(0.3)	0.2
Write-offs, Net of Recoveries	(2.0)	0.2	(1.3)
Balance at End of Year	$ 5.2	$ 3.5	$ 3.6