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Commitments and Contingencies - Contingencies and Litigation (Details) $ in Millions | 1 Months Ended |  |
--- | --- | --- | ---
Nov. 30, 2018 account | Sep. 30, 2021 USD ($) | Oct. 01, 2020 USD ($)
Loss Contingencies [Line Items] |  |  |
Loss contingency, range of possible loss, portion not accrued |  | $ 28.9 |
Maximum amount of individual accounts receivable account |  | $ 1.4 |
Cumulative Effect, Period of Adoption, Adjustment |  |  |
Loss Contingencies [Line Items] |  |  |
Retained earnings, before tax |  |  | $ 8.2
StoneX Financial |  |  |
Loss Contingencies [Line Items] |  |  |
Number of accounts | account | 300 |  |

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