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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Dec. 31, 2022 | Mar. 31, 2023 | Sep. 30, 2022
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |  |
Financial instruments sold, not yet purchased |  | $ 2,570.9 | $ 2,469.6
Interest rate contracts |  |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |  |
Maximum length of time hedged in cash flow hedge |  | 2 years |
Foreign currency forward contracts |  |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |  |
Maximum length of time hedged in cash flow hedge | 2 years | 2 years |
Fair Value, Recurring | Derivatives |  |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |  |
Financial instruments sold, not yet purchased |  | $ 209.7 | $ 313.4

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- Definition Fair value of obligations incurred from short sales. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 35 -Paragraph 1 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=35711043&loc=d3e42429-110968 + Details
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- Definition Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -URI https://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994 + 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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