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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, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |
Decrease in operating income | $ 11.1 | $ 9.9 | $ 11.0
Effect on net income or loss | $ (8.7) | $ (7.6) | $ (8.2)
Effect on earnings or loss per basic share | $ (0.06) | $ (0.05) | $ (0.05)
Effect on earnings or loss per diluted share | $ (0.06) | $ (0.05) | $ (0.05)

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- Definition Amount of expense for award under share-based payment arrangement. Excludes amount capitalized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 718 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479830/718-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 718 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
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