Stock-based Compensation Plans (Schedule of Share-based Compensation, Effect on Statement of Operations) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Decrease in operating income	$ 7.2	$ 5.5	$ 6.4
Effect on net income or loss	$ (5.0)	$ (4.3)	$ (4.0)
Effect on earnings or loss per basic share	$ (0.03)	$ (0.03)	$ (0.03)
Effect on earnings or loss per diluted share	$ (0.03)	$ (0.03)	$ (0.03)