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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Income Statement Effects of Derivative Instruments (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Designated as Hedging Instrument |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Total derivatives designated as hedging instruments | $ (44.7) | $ 2.4 |
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 | 109.0 | 100.4 | $ 80.8
Interest rate contracts | Designated as Hedging Instrument |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Total derivatives designated as hedging instruments | (47.0) | 2.4 |
Foreign currency forwards | Designated as Hedging Instrument |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Total derivatives designated as hedging instruments | $ 2.3 | $ 0.0 |

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- Definition Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Before Tax, Forecasted Transaction Not Probable + References No definition available. + Details
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Balance Type: | credit
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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 + 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 No definition available. + Details
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- Details
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- Details
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- Details
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