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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Schedule of Accumulated Other Comprehensive Income Effects of Derivative Instruments Designated for Hedging Held (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Amount of Gain/(Loss) Recognized in Other Comprehensive Income on Derivatives, net of tax | $ (0.6) | $ 25.7
Interest rate contracts |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Amount of Gain/(Loss) Recognized in Other Comprehensive Income on Derivatives, net of tax | 0.1 | 18.5
Foreign currency forwards |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Amount of Gain/(Loss) Recognized in Other Comprehensive Income on Derivatives, net of tax | $ (0.7) | $ 7.2

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