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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 (£)
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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 + Details
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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 + Details
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