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Acquisitions - R.J. O’Brien - Schedule of Aggregate Merger Consideration (Details) - USD ($) $ in Millions | Apr. 14, 2025 | Sep. 30, 2025 | Sep. 30, 2024
--- | --- | --- | ---
Purchase Price Allocation to Net Assets |  |  |
Goodwill |  | $ 298.3 | $ 61.0
RJO |  |  |
Business Combination [Line Items] |  |  |
Cash consideration | $ 651.9 |  |
Amounts receivable from sellers | (10.0) |  |
Total merger consideration | 942.0 |  |
Purchase Price Allocation to Net Assets |  |  |
Cash and cash equivalents | 162.5 |  |
Cash, securities and other assets segregated under federal and other regulations | 2,182.0 |  |
Securities purchased under agreements to resell | 1,581.2 |  |
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net | 3,287.7 |  |
Receivable from clients, net | 25.6 |  |
Financial instruments owned, at fair value | 30.6 |  |
Deferred tax asset | (0.5) |  |
Property and equipment, net | 14.9 |  |
Operating right of use assets | 6.4 |  |
Other assets | 54.9 |  |
Total fair value of tangible assets acquired | 7,345.3 |  |
Accounts payable and other accrued liabilities | 118.0 |  |
Operating lease liabilities | 11.3 |  |
Payable to clients | 6,637.2 |  |
Payables to lenders under loans | 125.7 |  |
Income taxes payable | 0.8 |  |
Deferred tax liabilities | 95.3 |  |
Total fair value of liabilities assumed | 6,988.3 |  |
Fair value of tangible net assets acquired | 357.0 |  |
Total fair value of intangible assets acquired | 410.6 |  |
Fair value of identifiable net assets acquired | 767.6 |  |
Total merger consideration | 942.0 |  |
Goodwill | 174.4 |  |
RJO | Client base |  |  |
Purchase Price Allocation to Net Assets |  |  |
Total fair value of intangible assets acquired | 407.7 |  |
RJO | Trade/domain names and other licenses |  |  |
Purchase Price Allocation to Net Assets |  |  |
Total fair value of intangible assets acquired | 2.9 |  |
RJO | Common Stock |  |  |
Business Combination [Line Items] |  |  |
Common stock | $ 300.1 |  |

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