Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Jun. 30, 2017	Sep. 30, 2016
Current assets:
Allowance for doubtful accounts	$ 0.4	$ 0.5
Stockholders' Equity Attributable to Parent [Abstract]
Preferred stock, par value (in dollars per share)	$ 0	$ 0
Preferred stock, shares authorized	25.0	25.0
Preferred stock, shares issued	0.0	0.0
Common stock, par value (in dollars per share)	$ 0.25	$ 0.25
Common stock, shares authorized	525.0	525.0
Common stock, shares issued	225.6	222.5
Common stock, shares outstanding	183.7	184.9