Consolidated Balance Sheets (unaudited) (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 13.6	$ 11.6
Accumulated depreciation	$ 1,488.0	$ 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)	66,735,745	66,792,968
Treasury stock, at cost (shares)	10,720,888	10,663,659