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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Schedule of Effects of Derivative Instruments Designated for Hedging Held (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives designated as hedging instruments	$ (17.1)	$ (44.7)
Amount of gain reclassified from accumulated other comprehensive income into income as a result of a forecasted transaction that is no longer probable of occurring	0.0	0.0
Interest rate contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives designated as hedging instruments	100.2	109.0	$ 100.4
Interest rate contracts | Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives designated as hedging instruments	(26.7)	(47.0)
Foreign currency forwards | Designated as Hedging Instrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives designated as hedging instruments	$ 9.6	$ 2.3

X

- Definition

Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Before Tax, Forecasted Transaction Not Probable

+ References

No definition available.

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- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

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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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