Pension Benefit Obligations - Equity Recognition (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
United States
Reconciliation of amounts in consolidated statements of stockholders' equity:
Prior service cost	$ (0.1)	$ (0.1)	$ (0.1)
Net loss	(77.5)	(91.7)	(116.5)
Total recognized in accumulated other comprehensive loss	(77.6)	(91.8)	(116.6)
International
Reconciliation of amounts in consolidated statements of stockholders' equity:
Prior service cost	(1.2)	(1.2)	(1.6)
Net loss	(207.1)	(187.1)	(279.5)
Total recognized in accumulated other comprehensive loss	$ (208.3)	$ (188.3)	$ (281.1)

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-Publisher FASB
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
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-Topic 220
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-10A

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (j)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

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Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

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Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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