Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current assets
Allowance for doubtful accounts	$ 4.3	$ 4.4
Stockholders' equity
Treasury stock, shares (in shares)	40.3	27.3
Preferred Stock
Stockholders' equity
Preferred stock, par value per share (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	100.0	100.0
Preferred stock, shares issued (in shares)	0.0	0.0
Preferred stock, shares outstanding (in shares)	0.0	0.0
Series Common Stock
Stockholders' equity
Common stock, par value per share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	50.0	50.0
Common stock, shares issued (in shares)	0.0	0.0
Common stock, shares outstanding (in shares)	0.0	0.0
Common Stock
Stockholders' equity
Common stock, par value per share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	450.0	450.0
Common stock, shares issued (in shares)	139.1	137.7
Common stock, shares outstanding (in shares)	98.8	110.4