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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Schedule of Notional Values of Derivative Instruments Designated for Hedging Held (Details) - Designated as Hedging Instrument £ in Millions, zł in Millions, $ in Millions	Sep. 30, 2025 USD ($)	Sep. 30, 2025 PLN (zł)	Sep. 30, 2025 GBP (£)	Sep. 30, 2024 USD ($)	Sep. 30, 2024 PLN (zł)	Sep. 30, 2024 GBP (£)
Interest rate contracts
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	$ 0.0			$ 500.0
Foreign currency forwards | Polish Zloty
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	45.0	zł 180.0		37.5	zł 156.1
Foreign currency forwards | British Pound Sterling
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Derivative, notional amount	$ 120.4		£ 93.0	$ 88.8		£ 72.0

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- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 181
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-181

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

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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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 940
-SubTopic 320
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/940-320/tableOfContent

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