Consolidated Balance Sheets (unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 11.7	$ 11.6
Accumulated depreciation	$ 1,495.1	$ 1,482.8
Common stock issued, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock issued, shares authorized (in shares)	300,000,000	300,000,000
Common stock issued, shares outstanding (in shares)	66,915,399	66,792,968
Treasury stock, at cost (shares)	10,541,234	10,663,659