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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
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Decrease in operating income	$ 11.0	$ 7.2	$ 5.5
Effect on net income or loss	$ (8.0)	$ (5.5)	$ (4.3)
Effect on earnings or loss per basic share	$ (0.05)	$ (0.03)	$ (0.03)
Effect on earnings or loss per diluted share	$ (0.05)	$ (0.03)	$ (0.03)

X

- Definition

Share-based Compensation, Increase (Decrease) in Earnings Per Share, Basic

+ References

No definition available.

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- Definition

Share-based Compensation, Increase (Decrease) in Earnings Per Share, Diluted

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
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-Topic 718
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- Definition

Amount, after tax, of expense for award under share-based payment arrangement.

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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.

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