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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 | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] | Cost of sales of physical commodities, Total revenues | Cost of sales of physical commodities, Total revenues | Cost of sales of physical commodities, Total revenues
Commodities |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments, gain (loss) recognized in income, net | $ 446.5 | $ 303.7 | $ 207.8
Foreign exchange |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments, gain (loss) recognized in income, net | 269.2 | 174.4 | 116.3
Interest rate contracts |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments, gain (loss) recognized in income, net | 109.0 | 100.4 | 80.8
TBA and forward settling securities |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments, gain (loss) recognized in income, net | 73.0 | 226.8 | (6.3)
Derivatives |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Derivative instruments, gain (loss) recognized in income, net | $ 897.7 | $ 805.3 | $ 398.6

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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 Indicates line item in statement of income or comprehensive income that includes gain (loss) from derivative. + 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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