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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
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Dec. 31, 2023 | Dec. 31, 2022
Commodities |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative instruments, gain (loss) recognized in income, net | $ 87.1 | $ 54.2
Foreign exchange |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative instruments, gain (loss) recognized in income, net | 25.2 | 48.8
Interest rate, equities, and indices |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative instruments, gain (loss) recognized in income, net | 27.4 | 8.3
TBA and forward settling securities |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative instruments, gain (loss) recognized in income, net | (93.2) | (23.0)
Derivatives |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Derivative instruments, gain (loss) recognized in income, net | $ 46.5 | $ 88.3

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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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