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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Realized Gains/Losses on Derivative Contracts (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023
Commodities |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net | $ 189.6 | $ 105.3 | $ 320.3 | $ 307.3
Foreign exchange |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net | 29.8 | (10.8) | 87.6 | (34.8)
Interest rate, equities, and indices |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net | 27.1 | 51.6 | 70.0 | 85.5
TBA and forward settling securities |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net | 8.7 | 42.0 | (59.0) | 4.9
Derivatives |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative instruments, gain (loss) recognized in income, net | $ 255.2 | $ 188.1 | $ 418.9 | $ 362.9

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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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-4E + Details
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