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Stock-based Compensation Plans (Schedule of Share-based Compensation, Effect on Statement of Operations) (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
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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)

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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