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consideration includes remeasurement of contingent liabilities related to business combinations accounted for in accordance with the provisions of the Business Combinations Topic of the ASC. 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O'Brien & Associates, LLC Subordinated Credit Facility R.J. O’Brien & Associates, LLC Subordinated [Member] R.J. O’Brien & Associates, LLC Subordinated Net income Net income Net income Net Income (Loss) Attributable to Parent Securities purchased under agreements to resell Increase (Decrease) in Receivables under Repurchase Agreements Timing of Transfer of Good or Service [Axis] Timing of Transfer of Good or Service [Axis] Allowance charge-offs SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Sales of physical commodities Revenue Not from Contract with Customer Preferred stock - authorized (in shares) Preferred Stock, Shares Authorized Adoption Date Trading Arrangement Adoption Date Trade conversion fees Trade Conversion Fees [Member] Trade Conversion Fees [Domain] Customer [Axis] Customer [Axis] Client and supplier base Customer Relationships [Member] Line of Credit Line of Credit [Member] Retained earnings Retained Earnings (Accumulated Deficit) Debt instrument offering price, percentage Debt Instrument, Discount Rate at Issuance of Face Value Debt Instrument, Discount Rate at Issuance of Face Value Non-cash equivalent segregated assets Non-cash Equivalent Segregated Assets Non-cash Equivalent Segregated Assets Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Time elapsed Transferred over Time [Member] Cash Flow Hedge Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Number of global financial markets (more than) Number Of Global Financial Markets Number Of Global Financial Markets Sean O’Connor Trading Arrangement, Stock Options [Member] Sean O’Connor Trading Arrangement, Stock Options Write off amortized intangible assets Impairment of Intangible Assets, Finite-Lived Securities and Other Assets Segregated Under Federal and Other Regulations [Axis] Securities and Other Assets Segregated Under Federal and Other Regulations [Axis] Securities and Other Assets Segregated Under Federal and Other Regulations [Axis] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Cash segregated and deposited with or pledged to exchange-clearing organizations and other futures commission merchants (“FCMs”) Cash Segregated And Deposited With Or Pledged To Exchange-clearing Organizations And Other Futures Commission Merchants Cash Segregated And Deposited With Or Pledged To Exchange-clearing Organizations And Other Futures Commission Merchants Payables to: Payables and Accruals [Abstract] Statement [Table] Statement [Table] Schedule of Aggregate Merger Consideration Business Combination [Table Text Block] Deferred income taxes Deferred Income Tax Expense (Benefit) Adjustments to reconcile net income to net cash provided by/(used in) operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Cash flows from financing activities: Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Commodities warehouse receipts Commodities Warehouse Receipts [Member] Commodities Warehouse Receipts [Member] All Adjustments to Compensation All Adjustments to Compensation [Member] Amendment Flag Amendment Flag StoneX Financial Inc. StoneX Financial Inc. StoneX Financial Inc. [Member] StoneX Financial Inc. [Member] Interest expense on corporate funding Interest Expense On Corporate Funding Interest Expense On Corporate Funding Common stock in treasury, at cost. 4,171,384 shares at March 31, 2026 and September 30, 2025 Treasury Stock, Common, Value Termination Date Trading Arrangement Termination Date Non segregated cash and other non cash equivalent assets included with in deposits and receivables from broker dealers clearing organizations and counter parties Non Segregated Cash And Other Non Cash Equivalent Assets Included With In Deposits And Receivables From Broker Dealers Clearing Organizations And Counter Parties Non Segregated Cash And Other Non Cash Equivalent Assets Included With In Deposits And Receivables From Broker Dealers Clearing Organizations And Counter Parties Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Raw materials Inventory, Raw Materials, Net of Reserves Operating revenue Business Combination, Acquiree's Revenue since Acquisition Date, Actual Basic (in shares) Common shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Schedule of Calculation of Numerator and Denominator in Earnings per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Segment Reporting [Abstract] Receivable from clients, net (including $52.4 million and $58.1 million at fair value at March 31, 2026 and September 30, 2025, respectively) Receivable from Customer in Brokerage Debt Disclosure [Abstract] Cash segregated under federal and other regulations Cash Segregated under Commodity Exchange Act Regulation Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Common stock - par value (in dollars per share) Common Stock, Par or Stated Value Per Share Derivative Instruments and Hedging Activities Disclosure [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Clients (including $(41.5) million and $530.7 million at fair value at March 31, 2026 and September 30, 2025, respectively) Broker-Dealer, Payable to Customer Use of Estimates Use of Estimates, Policy [Policy Text Block] Occupancy and equipment rental Occupancy, Net Compensatory damages awarded to other party Litigation Settlement, Amount Awarded to Other Party Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Domain] Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Domain] Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Domain] Insider Trading Arrangements [Line Items] Total fair value included in Payables to clients Payables To Clients [Member] Payables To Clients Non-variable expenses Non-Variable Expenses Non-Variable Expenses Equity securities Equity securities Equity Securities [Member] StoneX Financial Pte. Ltd. StoneX Financial Pte. Ltd. StoneX Financial Pte Ltd [Member] StoneX Financial Pte Ltd Total liabilities Liabilities Currency [Axis] Currency [Axis] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Client account fees Client Account Fees [Member] Client Account Fees [Member] Common stock, $0.01 par value. Authorized 200,000,000 shares; 83,200,883 issued and 79,029,499 outstanding at March 31, 2026 and 82,451,337 issued and 78,279,953 outstanding at September 30, 2025 Common Stock, Value, Outstanding Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Securities borrowed Securities borrowed, net Securities Borrowed Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Amounts receivable from sellers Business Combination, Consideration Transferred, Amounts Receivable From Sellers Business Combination, Consideration Transferred, Amounts Receivable From Sellers Deferred payments on acquisitions Payment for Deferred Contingent Consideration Liability, Financing Activities Payment for Deferred Contingent Consideration Liability, Financing Activities Asset-backed obligations Asset-backed obligations Asset-Backed Securities [Member] Consolidation Items [Axis] Consolidation Items [Axis] Bad debt expense (reversal) SEC Schedule, 12-09, Valuation Allowances and Reserves, Credit Loss Expense (Reversal) Not Included in Allowance SEC Schedule, 12-09, Valuation Allowances and Reserves, Credit Loss Expense (Reversal) Not Included in Allowance Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Commission and clearing fees Total commission and clearing fees Commission and Clearing Fees [Member] Commission and Clearing Fees [Member] Non-NEOs Non-NEOs [Member] Securities received as collateral that may be repledged Fair Value of Securities Received as Collateral that Can be Resold or Repledged Clearing fees Clearing Service [Member]