Income Taxes - Gross Unrecognized (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits
Balance at the beginning of the year	$ 55.2	$ 46.4
Gross increase in current period's tax positions	3.5	17.4
Gross increase in prior years' tax positions	17.9	2.4
Gross decrease in prior years' tax positions	(13.3)	(8.0)
Decrease due to settlement with tax authorities	(1.0)	(1.4)
Decrease due to lapse of statute of limitations		(0.5)
Gross change due to foreign exchange fluctuations	(0.2)	(1.1)
Balance at the end of the year	62.1	55.2
Income Taxes, additional disclosures
Accrued interest, excluding any related income tax benefits	24.4	20.5
Accrued penalties, excluding any related income tax benefits	$ 1.5	$ 1.7

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Amount of increase (decrease) in unrecognized tax benefits resulting from foreign currency translation.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Name Accounting Standards Codification
-Section 50
-Paragraph 15A
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-15A

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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- Definition

Amount of statutory penalties accrued for a tax position claimed or expected to be claimed by the entity, in its tax return.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of interest expense accrued for an underpayment of income taxes.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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