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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Gross Derivative Assets and Liabilities by Type and Balance Sheet Location (Details) contract in Millions, $ in Millions | Mar. 31, 2025 USD ($) contract | Sep. 30, 2024 USD ($) contract
--- | --- | ---
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | $ 6,149.0 | $ 7,235.9
Derivative liability, fair value, gross liability | 5,935.7 | 7,144.1
Impact of netting and collateral asset | (6,006.0) | (6,670.6)
Impact of netting and collateral liability | $ (5,956.8) | $ (6,614.6)
Derivative, number of instruments held | contract | 12.8 | 12.2
Total fair value included in Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | $ (72.4) | $ 336.0
Total fair value included in Receivable from clients, net |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | 0.5 | (8.4)
Total fair value included in Financial instruments owned, at fair value |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | 214.9 | 237.7
Total fair value included in Payables to clients |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | (215.4) | 265.9
Total fair value included in Payables to broker-dealers, clearing organizations and counterparties |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | (11.2) | (1.4)
Total fair value included in Financial instruments sold, not yet purchased, at fair value |  |
Derivatives, Fair Value [Line Items] |  |
Derivative, fair value, net | 205.5 | 265.0
Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 6,139.9 | 7,226.3
Derivative liability, fair value, gross liability | 5,935.5 | 7,143.9
Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 9.1 | 9.6
Derivative liability, fair value, gross liability | 0.2 | 0.2
Exchange-traded commodity derivatives | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 1,588.4 | 1,383.1
Derivative liability, fair value, gross liability | 1,612.9 | 1,415.7
OTC commodity derivatives | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 2,651.9 | 1,967.9
Derivative liability, fair value, gross liability | 2,467.9 | 1,924.3
Exchange-traded foreign exchange derivatives | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 4.2 | 2.0
Derivative liability, fair value, gross liability | 4.2 | 2.0
OTC foreign exchange derivatives | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 453.7 | 975.2
Derivative liability, fair value, gross liability | 437.2 | 938.2
Exchange-traded interest rate derivatives | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 656.6 | 720.1
Derivative liability, fair value, gross liability | 658.7 | 728.1
OTC interest rate derivatives | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 180.1 | 207.1
Derivative liability, fair value, gross liability | 180.1 | 207.1
OTC interest rate derivatives | Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 0.0 | 0.0
Derivative liability, fair value, gross liability | 0.0 | 0.2
Exchange-traded equity index derivatives | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 381.6 | 1,817.4
Derivative liability, fair value, gross liability | 381.6 | 1,817.4
OTC equity and indices derivatives | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 201.4 | 127.4
Derivative liability, fair value, gross liability | 171.2 | 86.7
TBA and forward settling securities | Not Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 22.0 | 26.1
Derivative liability, fair value, gross liability | 21.7 | 24.4
Foreign currency forward contracts | Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Derivative asset, fair value, gross asset | 9.1 | 9.6
Derivative liability, fair value, gross liability | $ 0.2 | $ 0.0

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