Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Capital and Other Regulatory Requirements [Abstract] Capital and Other Regulatory Requirements [Abstract] Capital and Other Regulatory Requirements [Abstract] Actuarial gain on pension and postretirement benefits Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) U.S. state and local Current State and Local Tax Expense (Benefit) Number of Shares Outstanding, Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Consolidated Entities [Axis] Consolidated Entities [Axis] Securities sold under agreements to repurchase Increase (Decrease) in Payables under Repurchase Agreements Schedule of Aggregate Merger Consideration Schedule of Business Acquisitions, by Acquisition [Table Text Block] Basic earnings per share (in dollars per share) Business Acquisition, Pro Forma Earnings Per Share, Basic Income taxes payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Income Taxes Payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Income Taxes Payable Number of options to renew (or more) Lessee, Operating Lease, Minimum Number Of Options To Renew Lessee, Operating Lease, Minimum Number Of Options To Renew Preferred stock - outstanding (in shares) Preferred Stock, Shares Outstanding Defined contribution plan, employers matching contribution, annual vesting percentage, three to four years Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, Three to Four Years Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, Three to Four Years Goodwill Goodwill Disclosure [Text Block] US government securities and other securities - deposits and receivables US Government Securities and Other Securities - Deposits and Receivables US Government Securities and Other Securities - Deposits and Receivables Notes payable to bank Notes Payable to Bank Debt instrument, conversion price (in dollars per share) Debt Instrument, Convertible, Conversion Price Weighted Average Grant Date Fair Value, Forfeited (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Deferred payments on acquisitions Payment for Contingent Consideration Liability, Financing Activities Payable to broker-dealers, clearing organizations, and counterparties Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Stock options forfeited in period (in shares) Number of options outstanding, forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Weighted average remaining lease term (years) Operating Lease, Weighted Average Remaining Lease Term Foreign Currency Translation Foreign Currency Transactions and Translations Policy [Policy Text Block] Exchange-traded commodity derivatives Exchange-traded Commodity Contracts [Member] Exchange-traded Commodity Contracts [Member] Stock options authorized (in shares) Shares available for grant, Beginning (in shares) Shares available for grant, Ending (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Net increase in cash, segregated cash, cash equivalents, and segregated cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Proceeds from stock sales of clearing organization memberships Proceeds From Stock Sales Of Clearing Organization Memberships Proceeds From Stock Sales Of Clearing Organization Memberships Interest income Interest Income, Operating Acquired Finite-Lived Intangible Assets [Line Items] Acquired Finite-Lived Intangible Assets [Line Items] Expected stock price volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Denominator: Denominator Basic [Abstract] Denominator Basic Cash held at banks and money market funds - segregated Cash Held at Banks and Money Market Funds - Segregated Cash Held at Banks and Money Market Funds - Segregated Number of employees Entity Number of Employees Business acquisition, premium amount Business Acquisition, Purchase Price In Excess Of Net Book Value Premium Business Acquisition, Purchase Price In Excess Of Net Book Value Premium Income taxes payable Increase (Decrease) in Income Taxes Payable Share-based compensation arrangement by share-based payment award, options, exercises in period, total intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Certificates of deposit Certificates of Deposit [Member] Cash reserve deposit required and made Cash Reserve Deposit Required and Made Recovery of Bad Debt on Physical Coal [Abstract] Recovery of Bad Debt on Physical Coal [Abstract] Recovery of Bad Debt on Physical Coal Document Fiscal Year Focus Document Fiscal Year Focus Exercise price range, lower range limit Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit Provision for (recovery of) bad debts SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Other Other Consulting, Management, and Account Fees [Member] Other Consulting, Management, and Account Fees [Member] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Retirement Benefits - Defined Contribution Plans [Abstract] Retirement Benefits - Defined Contribution Plans [Abstract] Retirement Benefits - Defined Contribution Plans [Abstract] Amortization of intangible assets Amortization of Intangible Assets Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Total excess purchase price allocated to identifiable intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Acquired finite-lived intangible asset, weighted average useful life Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Debt Securities Defined Benefit Plan, Debt Security [Member] Proceeds from issuance of senior secured notes Proceeds from Issuance of Senior Long-term Debt Deferred income taxes, net Deferred Tax Assets, Net Weighted average discount rate Operating Lease, Weighted Average Discount Rate, Percent Schedule of Inventory Schedule of Inventory, Current [Table Text Block] Antidilutive securities (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Repayments of lenders under loans with maturities greater than 90 days Repayments of Short-term Debt, Maturing in More than Three Months Securities loaned Increase (Decrease) in Securities Loaned Transactions Purchase price allocated to property and equipment acquired Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment Business Combination and Asset Acquisition [Abstract] Deferred tax assets Deferred Tax Assets, Net of Valuation Allowance Number of commercial and institutional clients (more than) Number of Commercial and Institutional Clients Number of Commercial and Institutional Clients Cash, Securities and Other Assets Segregated under Federal and other Regulations Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Business Acquisition [Axis] Business Acquisition [Axis] Condensed Cash Flow Statement [Table] Condensed Cash Flow Statement [Table] Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding Receivables from clients Income tax receivable Business Combination, Acquired Receivable, Fair Value Collateralized transactions: Collateralized Financings [Abstract] Business combination, convertible senior notes redeemed amount Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Amount Redeemed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Amount Redeemed Stock Option Activity, Additional Disclosures Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Number of options outstanding, exercisable (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Bad debts, net of recoveries and impairment Provision for bad debts, net of recoveries and impairment Accounts Receivable, Credit Loss Expense (Reversal) And Impairment Accounts Receivable, Credit Loss Expense (Reversal) And Impairment Goodwill and Identifiable Intangible Assets Goodwill and Intangible Assets, Policy [Policy Text Block] Finite-lived intangible assets acquired Finite-lived Intangible Assets Acquired Physical Commodities Inventory [Axis] Physical Commodities Inventory [Axis] Physical Commodities Inventory [Axis] Retained Earnings Retained Earnings [Member] Recovery of Bad Debt on Physical Coal Unusual or Infrequent Items, or Both, Disclosure [Text Block] Corporate and municipal bonds Debt Securities [Member] Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties [Axis] Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties [Axis] Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties [Axis] $20.00 - $25.00 Exercise Price Range Five [Member] Exercise Price Range Five [Member] Receivable from clients, net Increase (Decrease) in Accounts Receivable Germany GERMANY Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Debt, weighted average interest rate Debt, Weighted Average Interest Rate Payable to subsidiaries, net Due to Related Parties $35.00 - $40.00 Exercise Price Range Eight [Member] Exercise Price Range Eight [Member] Receivables from clients, net - Derivatives Accounts Receivable, Fair Value Disclosure Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract] Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract] Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract] Compensation and Benefits Compensation Related Costs, Policy [Policy Text Block] Brazil BRAZIL Basic (in dollar per share) Earnings Per Share, Basic Revenue from Contract with Clients Revenue from Contract with Customer [Text Block] Trademarks/domain names Trademarks And Domain Names [Member] Trademarks And Domain Names Number of Shares Outstanding, Beginning (in shares) Number of Shares Outstanding, Ending (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Document Type Document Type Other Total other expenses Other Noninterest Expense Geographic Concentration Risk Geographic Concentration Risk [Member] IFFI Uncommitted Lines of Credit IFFI Uncommitted Lines of Credit [Member] IFFI Uncommitted Lines of Credit Entity Current Reporting Status Entity Current Reporting Status Equity investments in exchange stock - cost Equity Investments in Exchange Stock - Cost Equity Investments in Exchange Stock - Cost Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net (including $1,070.6 million and $1,775.8 million at fair value at September 30, 2021 and 2020, respectively) Receivables from Brokers-Dealers and Clearing Organizations Cumulative Effect, Period of Adoption, Adjustment Cumulative Effect, Period of Adoption, Adjustment [Member] Principal gains, net Principal Transactions Revenue, Net Derivative asset, fair value, gross asset Derivative Asset, Fair Value, Gross Asset ARGENTINA ARGENTINA Percentage of required net capital under commodity exchange act Futures Commission Merchant, Commodity Exchange Act, Required Net Capital, Percent Of Liabilities Owed to Counterparties Futures Commission Merchant, Commodity Exchange Act, Required Net Capital, Percent Of Liabilities Owed to Counterparties Australia AUSTRALIA Securities borrowed Increase (Decrease) in Securities Borrowed IFCM Commodities Acquisition IFCM Commodities Acquisition [Member] IFCM Commodities Acquisition Foreign currency gains realized upon dissolution of subsidiaries (included in principal gains, net) Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax Depreciation and amortization Other Depreciation and Amortization Schedule of Revenue Long-Lived Assets, by Geographical Areas Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] Customer Lists And Relationships Customer Lists And Relationships [Member] Customer Lists And Relationships Liabilities acquired Noncash or Part Noncash Acquisition, Value of Liabilities Assumed Defined Benefit Plan, Plan Assets, Category [Domain] Defined Benefit Plan, Plan Assets, Category [Domain] Proceeds from issuance of senior secured term loan Proceeds from Issuance of Secured Debt Plan Name [Axis] Plan Name [Axis] Long-term debt Long-term Debt Level 1 Fair Value, Inputs, Level 1 [Member] Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Goodwill impairment charges Goodwill, Impairment Loss Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value [Roll Forward] Cash and securities segregated under commodity exchange act regulation Cash and Securities Segregated under Commodity Exchange Act Regulation Base Rate Base Rate [Member] Schedule of Allowance for Doubtful Accounts Financing Receivable, Allowance for Credit Loss [Table Text Block] Deferred compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Receivable from clients, net Accounts Receivable, after Allowance for Credit Loss Income taxes receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Income Taxes Receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Income Taxes Receivable Exchange-traded futures and options Exchange-Traded Futures and Options [Member] Exchange-Traded Futures and Options [Member] Additional paid-in-capital Additional paid-in capital Additional Paid in Capital Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets [Table Text Block] Underwriting fees Underwriting Fees [Member] Underwriting Fees [Member] GIROXX Gmbh GIROXX Gmbh [Member] GIROXX Gmbh Client payables at fair value Broker-Dealer, Payable to Customer, Fair Value Broker-Dealer, Payable to Customer, Fair Value LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Agency mortgage-backed obligations Collateralized Mortgage Backed Securities [Member] Additional consideration payable related to acquisitions Noncash or Part Noncash Acquisition, Additional Consideration Payable Noncash or Part Noncash Acquisition, Additional Consideration Payable Fiscal 2025 Finite-Lived Intangible Asset, Expected Amortization, Year Four TBA and forward settling securities TBA and Forward Settling Securities [Member] TBA and Forward Settling Securities [Member] Interest Expense Interest Expense, Policy [Policy Text Block] Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Securities borrowed, gross Securities Borrowed, Gross Contingent consideration, liability Additional consideration payable related to acquisitions Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability Balance Sheet Location [Domain] Balance Sheet Location [Domain] Receivable from affiliate Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Receivable From Affiliate Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Receivable From Affiliate Securities loaned Securities loaned Securities Loaned Total gross deferred tax assets Deferred Tax Assets, Gross Fair value of tangible net assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Tangible Assets, Net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Tangible Assets, Net Trading Symbol Trading Symbol Securities sold under agreements to repurchase, gross Securities Sold under Agreements to Repurchase, Gross Reclassification adjustment for gains/(losses) included in net income Amounts reclassified from AOCI, net of tax Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent Deferred income taxes, net Deferred Income Tax Assets, Net United Kingdom UNITED KINGDOM Term loan periodic principal payment percentage Term Loan Periodic Principal Payment Percentage Term Loan Periodic Principal Payment Percentage Management services fees to affiliates Management Fee Expense TBA Securities Purchased, Unrealized Loss TBA Securities Purchased, Unrealized Loss [Member] TBA Securities Purchased, Unrealized Loss Revision of Prior Period [Axis] Revision of Prior Period [Axis] Weighted average  exercise price, exercisable (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price StoneX Financial Margin line of credit facility FCS Margin Line Of Credit Facility [Member] FCS Margin line of credit facility Physical Commodities Inventory Inventory Disclosure [Text Block] Equity securities Equity Securities [Member] Accounting Policies [Abstract] Accounting Policies [Abstract] Defined benefit plan, expected future benefit payment, year four Defined Benefit Plan, Expected Future Benefit Payment, Year Four Foreign government obligations Debt Security, Government, Non-US [Member] Weighted average remaining term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Derivative Instrument Risk [Axis] Derivative Instrument [Axis] Other assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets Forward Settling Securities Sold, Unrealized Gain Forward Settling Securities Sold, Unrealized Gain [Member] Forward Settling Securities Sold, Unrealized Gain U.S. federal Current Federal Tax Expense (Benefit) Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties [Domain] Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties [Domain] Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties Operating lease liabilities Present value of lease liabilities Operating Lease, Liability Broker-dealers, clearing organizations and counterparties (including $12.7 million and $14.7 million at fair value at September 30, 2021 and 2020, respectively) Payable to broker-dealers, clearing organizations and counterparties Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization Net income Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Employee service share-based compensation, non vested awards, total compensation cost not yet recognized, period for recognition Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Weighted Average Grant Date Fair Value, Beginning (in dollar per share) Weighted Average Grant Date Fair Value, Ending (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Physical precious metals trading Precious Metals Trading [Member] Precious Metals Trading Member Percentage of stop loss actual estimated claims Self Insurance, Stop Loss Coverage, Claims Threshold, Percent Self Insurance, Stop Loss Coverage, Claims Threshold, Percent Leases Lessee, Operating Leases [Text Block] Defined benefit plan, funded (unfunded) status of plan Defined Benefit Plan, Funded (Unfunded) Status of Plan Forward Settling Securities Sold, Unrealized Loss Forward Settling Securities Sold, Unrealized Loss [Member] Forward Settling Securities Sold, Unrealized Loss Acquisitions Business Combination Disclosure [Text Block] TBA Securities Purchased, Unrealized Gain TBA Securities Purchased, Unrealized Gain [Member] TBA Securities Purchased, Unrealized Gain Finite-lived customer base, gross amount Finite-Lived Customer Lists, Gross Schedule of Share-based Payment Award, Stock options, Valuation Assumptions Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Other international Deferred Foreign Income Tax Expense (Benefit) Share-based awards (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Goodwill [Line Items] Goodwill [Line Items] Net income Business Acquisition, Pro Forma Net Income (Loss) Secured funds required under commodity exchange act Secured Funds Required Under Commodity Exchange Act Secured Funds Required Under Commodity Exchange Act Total income tax expense Income Tax Expense (Benefit), Intraperiod Tax Allocation Schedule of Other Operating Cost and Expense, by Component Schedule of Other Operating Cost and Expense, by Component [Table Text Block] Aggregate cash consideration Payments to Acquire Productive Assets $15.00 - $20.00 Exercise Price Range Four [Member] Exercise Price Range Four [Member] Payable to clients Financial instruments sold, not yet purchased, at fair value Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Share-based Payment Arrangement, Option, Exercise Price Range [Line Items] Share-based compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Precious metals - held by non -broker -dealer subsidiaries Inventory, Finished Goods, Net of Reserves UOB Bullion and Futures Limited UOB Bullion and Futures Limited [Member] UOB Bullion and Futures Limited Consolidation Items [Domain] Consolidation Items [Domain] Equity: Equity [Abstract] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Comprehensive Income Comprehensive Income, Policy [Policy Text Block] Financial instruments owned, at fair value (includes securities pledged as collateral that can be sold or repledged of $843.3 million and $468.6 million at September 30, 2021 and 2020, respectively) Financial instruments, owned, at fair value Financial Instruments, Owned, at Fair Value Property and equipment Deferred Tax Assets, Property, Plant and Equipment Netting Counterparty And Cash Collateral Netting Adjustment [Member] Counterparty And Cash Collateral Netting Adjustment Gross fair value of derivative contracts Derivative Liability, Collateral, Right to Reclaim Cash, Offset Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Secured funds Secured Funds Secured funds Variable Rate [Axis] Variable Rate [Axis] Segment and Geographic Information Segment Reporting Disclosure [Text Block] Other comprehensive income OCI, before Reclassifications, Net of Tax, Attributable to Parent Notes Receivable Financing Receivable [Policy Text Block] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Consulting, management and account fees Total consulting, management, and account fees Consulting, Management And Account Fees [Member] Consulting, Management And Account Fees Debt instrument, face amount Term Loan Initial Balance Term Loan Initial Balance Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties Deposits and Receivables from Broker-dealers, clearing organizations and counterparties [Member] Deposits and Receivables from Broker-dealers, clearing organizations and counterparties [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Consulting fee Consulting Fee [Member] Consulting Fee Variable Rate [Domain] Variable Rate [Domain] Gain on acquisitions and other gains Gain on acquisitions Gain (Loss) On Acquisitions And Other Gain (Loss) On Acquisitions And Other StoneX Inc. Bank of America Syndicated Credit Facility StoneX Inc. Bank of America Syndicated Credit Facility [Member] StoneX Inc. Bank of America Syndicated Credit Facility Additional Paid-in Capital Additional Paid-in Capital [Member] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Defined benefit plan, expected future benefit payment, five fiscal years thereafter Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years PAB SRBA PAB SRBA [Member] PAB SRBA Operating revenues post-acquisition results of the acquired business Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Gross fair value of derivative contracts Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Regulatory Requirements and Subsidiary Dividend Restrictions Regulatory Capital Requirements under Banking Regulations [Text Block] Trading systems and market information Trading Systems And Market Information Trading Systems And Market Information Notes receivable, net Financing Receivable, after Allowance for Credit Loss Long-term debt, fair value Long-term Debt, Fair Value Notes receivable, net Increase (Decrease) in Finance Receivables Weighted average grant date fair value, Beginning (in dollar per share) Weighted average grant date fair value, Ending (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value The weighted average grant-date fair value of options outstanding as calculated by applying the disclosed option pricing methodology. Debt instrument, redemption price, percentage of principal amount redeemed Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed Right of use assets, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Right Of Use Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Right Of Use Assets $40.00 - $45.00 Exercise Price Range Nine [Member] Exercise Price Range Nine [Member] Maximum Maximum [Member] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Share-based Payment Arrangement [Abstract] Purchase obligation, due in fourth and fifth year Purchase Obligation, to be Paid, Year Four and Five Rabobank Uncommited Line of Credit Rabobank Uncommited Line of Credit [Member] Rabobank Uncommited Line of Credit Legal Entity [Axis] Legal Entity [Axis] $25.00 - $30.00 Exercise Price Range Six [Member] Exercise Price Range Six [Member] US government obligations and other securities US Government Obligations and other securities US Government Obligations and other securities - Segregated Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Schedule of Operating Lease, Liability, Maturity Lessee, Operating Lease, Liability, Maturity [Table Text Block] Total equity Beginning balance Ending balance Stockholders' Equity Attributable to Parent Schedule of Assets Sold under Agreements to Repurchase [Table] Schedule of Assets Sold under Agreements to Repurchase [Table] Accounts payable and other accrued liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Due to/from subsidiaries Increase (Decrease) Due from Affiliates Other assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets Aggregate intrinsic value, exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Number of options outstanding, exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Document Annual Report Document Annual Report Repayment of senior secured notes Repayments of senior secured notes Repayments of Senior Debt Intangible Assets Intangible Assets Disclosure [Text Block] Share repurchase Payments for Repurchase of Common Stock Property plant and equipment, useful life Property, Plant and Equipment, Useful Life Deposits with and receivables from broker-dealers, clearing organizations, and counterparties Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Receivables From Broker-dealers, Clearing Organizations, And Counterparties Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Receivables From Broker-dealers, Clearing Organizations, And Counterparties Business acquisition, share price (in dollars per share) Business Acquisition, Share Price Stockholders' equity: StoneX Group Inc. (Parent Company Only) stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Total revenues (percentage) Revenues from contracts with clients as a % of total revenues Revenues from contracts with clients as a % of total revenues Net operating revenues Net operating revenues (loss): Revenues, Net of Interest Expense Total current taxes Current Income Tax Expense (Benefit) Debt instrument, face amount Debt Instrument, Face Amount Net periodic benefit Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Less: Allocation to participating securities Undistributed Earnings Allocated to Participating Securities - Continuing Operations Undistributed Earnings Allocated to Participating Securities - Continuing Operations represents earnings from continuing operations allocated (not distributed) to participating securities under the two-class method to the extent that participating securities may share in earnings as if all of the earnings for the period had been distributed. UK Plan UK Plan [Member] UK Plan [Member] Net liabilities denominated in argentine pesos Net Liabilities Denominated In Argentine Pesos Net Liabilities Denominated In Argentine Pesos TBA Securities Sold, Unrealized Gain TBA Securities Sold, Unrealized Gain [Member] TBA Securities Sold, Unrealized Gain Operating Segments Operating Segments [Member] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Weighted average grant date fair value, exercisable (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Grant Date Fair Value The weighted average grant-date fair value of options excercisable as calculated by applying the disclosed option pricing methodology. Line of credit facility, unused capacity, commitment fee percentage Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Schedule of Preliminary Purchase Price Allocation as of the Acquisition Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Revision of Prior Period [Domain] Revision of Prior Period [Domain] Schedule of Condensed Financial Statements [Table] Condensed Financial Statements [Table] 30-90 Days Maturity 30 to 90 Days [Member] Deferred income tax liabilities Deferred Tax Liabilities, Gross Business Acquisition [Line Items] Business Acquisition [Line Items] Equity Securities Defined Benefit Plan, Equity Securities [Member] Income Statement [Abstract] Income Statement [Abstract] Asset Class [Domain] Asset Class [Domain] Diluted earnings per share (in dollars per share) Business Acquisition, Pro Forma Earnings Per Share, Diluted Number of countries in which entity operates (more than) Number of Countries in which Entity Operates Receivables from clients, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Reclassification of adjustment for losses/(gains) included in net income: Reclassification of adjustment for gains included in net income [Abstract] Reclassification of adjustment for gains included in net income [Abstract] Allowance charge-offs SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Financial Instrument Sold, Not Yet Purchased Financial Instrument Sold, Not Yet Purchased [Member] Financial Instrument Sold, Not Yet Purchased [Member] Numerator: Numerator Basic [Abstract] Numerator Basic Weighted average exercise price (in dollars per share) Share-based Payment Arrangement, Option, Exercise Price Range, Outstanding, Weighted Average Exercise Price Weighted average  exercise price, forfeited (in dollar per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Income tax expense Income tax expense Income tax benefit Income Tax Expense (Benefit) Defined benefit plan, expected future benefit payment, year three Defined Benefit Plan, Expected Future Benefit Payment, Year Three Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Financial instruments owned, at fair value Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Assets Investment Type [Axis] Investment Type [Axis] Entity Voluntary Filers Entity Voluntary Filers Dividend income from subsidiaries SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Consolidated Subsidiaries Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block] TBA Securities Sold, Unrealized Loss TBA Securities Sold, Unrealized Loss [Member] TBA Securities Sold, Unrealized Loss Total lease payments Lessee, Operating Lease, Liability, to be Paid Number of Shares Outstanding, Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Travel and business development Travel and Entertainment Expense Time elapsed Transferred over Time [Member] Share-Based Compensation Share-based Payment Arrangement [Policy Text Block] Repurchase of stock Stock Repurchased During Period, Value Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Employee service share-based compensation, non vested awards, total compensation cost not yet recognized, stock options Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount Long-Lived Tangible Asset [Domain] Long-Lived Tangible Asset [Domain] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Entity Small Business Entity Small Business Securities Purchased under Agreements to Resell, Offset Securities Purchased under Agreements to Resell, Liability Schedule of Finite and Indefinite-Lived Intangible Assets Schedule of Finite and Indefinite-Lived Intangible Assets [Table Text Block] Tabular disclosure of assets, excluding financial assets and goodwill, lacking physical substance with a finite life or exist in perpetuity, by either major class or business segment. Forward Settling Securities Purchased, Unrealized Gain Forward Settling Securities Purchased, Unrealized Gain [Member] Forward Settling Securities Purchased, Unrealized Gain Net nonmonetary denominated in Argentine pesos Net Nonmonteary Assets Denominated in Argentine Pesos Net Nonmonteary Assets Denominated in Argentine Pesos Revenue Benchmark Revenue Benchmark [Member] Weighted average grant date fair value, granted (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Equity Component [Domain] Equity Component [Domain] Shares Available for Grant, Beginning (in shares) Shares Available for Grant, Ending (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number Securities and Commodity Financing Transactions Repurchase Agreements, Resale Agreements, Securities Borrowed, and Securities Loaned Disclosure [Text Block] Prepaid expenses Deferred Tax Liabilities, Prepaid Expenses Physical agricultural and energy product trading Agricultural And Energy Product Trading [Member] Agricultural And Energy Product Trading Member Defined contribution plan, employers matching contribution, annual vesting percentage Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage 2022 Lessee, Operating Lease, Liability, to be Paid, Year One Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Collateralized Transactions Repurchase and Resale Agreements Policy [Policy Text Block] Defined Benefit Plan, Plan Assets, Category [Axis] Defined Benefit Plan, Plan Assets, Category [Axis] Accounts payable and other accrued liabilities (including $2.8 million and $1.5 million at fair value at September 30, 2021 and 2020, respectively) Accounts payable and other accrued liabilities Accounts Payable and Other Accrued Liabilities Memberships in exchanges owned Memberships in Exchanges Owned Accrual for merger cash consideration Purchase of shareholders equity interest Business Combination, Consideration Transferred, Equity Interests Issued and Issuable Debt issuance costs, gross Debt Issuance Costs, Gross Additional Paid-In Capital Stockholders' Equity, Policy [Policy Text Block] Shares Available for Grant, Forfeited Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures Foreign tax credits, net Deferred Tax Assets, Net Of Valuation Allowance, Tax Credit Carryforwards, Foreign Deferred Tax Assets, Net Of Valuation Allowance, Tax Credit Carryforwards, Foreign Commercial Commercial Segment [Member] Commercial Segment Liabilities: Liabilities [Abstract] Change in valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent 2025 Lessee, Operating Lease, Liability, to be Paid, Year Four Intangible assets, gross amount Intangible Assets, Gross (Excluding Goodwill) Forward Settling Securities Purchased, Unrealized Loss Forward Settling Securities Purchased, Unrealized Loss [Member] Forward Settling Securities Purchased, Unrealized Loss Finanical Instruments Owned and Sold, Not yet Purchased Fair Value, Security Name [Domain] Security Owned and Sold, Not yet Purchased Fair Value, Security Name [Domain] Business combination, excess amount above book value of tangible assets acquired Business Combination, Excess Amount Above Book Value Of Tangible Assets Acquired Business Combination, Excess Amount Above Book Value Of Tangible Assets Acquired Income from operations, before tax Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Level 2 Fair Value, Inputs, Level 2 [Member] Derivative instruments, gain (loss) recognized in income, net Derivative, Gain (Loss) on Derivative, Net Segment Reporting [Abstract] Segment Reporting [Abstract] Chasing Returns Limited Chasing Returns Limited [Member] Chasing Returns Limited Other compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits Commodities Commodity Contract [Member] Use of Estimates Use of Estimates, Policy [Policy Text Block] Management fees from affiliates Management Fees From Affiliates [Member] Management Fees From Affiliates Minimum regulatory capital requirement Banking Regulation, Total Risk-Based Capital, Capital Adequacy, Minimum Schedule of Calculation of Numerator and Denominator in Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Other comprehensive gain/(loss) Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Foreign tax credit carryforwards Deferred Tax Assets, Tax Credit Carryforwards, Foreign Revision of Prior Period, Adjustment Revision of Prior Period, Adjustment [Member] Exchange Memberships not Representing an Ownership Interest Exchange memberships not representing an ownership interest [Member] Exchange memberships not representing an ownership interest [Member] Common stock - authorized (in shares) Common Stock, Shares Authorized Repayments of senior secured term loan Repayments of Secured Debt Singapore SINGAPORE Aggregated Merger Consideration Business Combination, Consideration Transferred [Abstract] Mutual funds Mutual Fund Trailing Commissions [Member] Mutual Fund Trailing Commissions [Member] Securities loaned, fair value of collateral Securities Loaned, Fair Value of Collateral Product and Service [Domain] Product and Service [Domain] Debt instrument, interest rate, stated percentage Debt Instrument, Interest Rate, Stated Percentage Renewal term Lessee, Operating Lease, Renewal Term Translation losses Amount Recognized in Income Due to Inflationary Accounting Fair value of contingent consideration Business Combination, Contingent Consideration, Liability StoneX, Ltd StoneX Financial Ltd. StoneX, Ltd [Member] StoneX, Ltd (IFEL) Tri-party Repurchase Agreements Repurchase Agreements [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Share-based Payment Arrangement, Option, Exercise Price Range [Table] Derivative liability, notional amount Derivative Liability, Notional Amount Lease, Cost Lease, Cost [Table Text Block] Corporate bonds Corporate Bond Securities [Member] Geographical [Axis] Geographical [Axis] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Amortization of operating right of use assets Operating Lease, Right-of-Use Asset, Amortization Expense $55.00 - $60.00 Exercise Price Range Twelve [Member] Exercise Price Range Twelve Total fair value of tangible assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Term of syndicated loan facility Line of Credit Facility, Expiration Period Clearing fees Clearing Service [Member] Term of risk management consulting contracts Revenue, Term Of Risk Management Consulting Contract Revenue, Term Of Risk Management Consulting Contract Financial Instruments Owned and Sold, Not Yet Purchased Investment, Policy [Policy Text Block] Number retail clients (more than) Number Retail Clients Number Retail Clients Net cash (used in)/provided by financing activities Net Cash Provided by (Used in) Financing Activities Common stock in treasury, at cost. 2,607,323 shares at September 30, 2021 and 2,421,957 shares at September 30, 2020 Treasury Stock, Value Physical Ag & Energy Agricultural Related Inventory Securities purchased under agreements to resell Securities purchased under agreements to resell Securities Purchased under Agreements to Resell Weighted Average Remaining Term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms Assets and Liabilities, at Fair Value Fair Value Disclosures [Text Block] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Other commitment, due in next twelve months Other Commitment, to be Paid, Year One Fiscal 2024 Finite-Lived Intangible Asset, Expected Amortization, Year Three Acquisitions and Contingent Consideration Business Combinations Policy [Policy Text Block] Defined contribution plan, employers matching contribution, annual vesting percentage, all years Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, All Years Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, All Years Adjustment to investment in subsidiaries for equity method accounting Adjustment to Investment in Subs for Equity Method Accounting Adjustment to Investment in Subs for Equity Method Accounting Accounts payable and other accrued liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Cash denominated in argentine pesos (less than) Cash denominated in Argentine Pesos Cash denominated in Argentine Pesos Revenues: Revenues [Abstract] Deferred income tax liabilities: Deferred Tax Liabilities, Net [Abstract] Weighted average grant date fair value, exercised (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Weighted Average Grant Date Fair Value The weighted average grant-date fair value of options excercised during the reporting period as calculated by applying the disclosed option pricing methodology. Software programs/platforms Software programs/platforms Computer Software, Intangible Asset [Member] Quest Capital Strategies Inc Quest Capital Strategies Inc [Member] Quest Capital Strategies Inc Capital contribution to affiliates Payments to Acquire Additional Interest in Subsidiaries Securities and other assets segregated under federal and other regulations Increase (Decrease) in Restricted Investments for Operating Activities Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Inventory [Domain] Inventory [Domain] Financial Instruments Owned and Sold, Not yet Purchased, at Fair Value [Axis] Security Owned and Sold, Not yet Purchased, at Fair Value [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Number of Options Outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] U.S. State and local income taxes Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent U.S. state and local Deferred State and Local Income Tax Expense (Benefit) Property, Plant and Equipment Property, Plant and Equipment [Table Text Block] Income Statement Location [Domain] Income Statement Location [Domain] Supplemental disclosure of non-cash investing and financing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Number of additional shares authorized (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Property and equipment, net Property and equipment, net Property, Plant and Equipment, Net Physical commodities inventory Physical Commodities Inventory - Precious Metals Physical Commodities Inventory - Precious Metals [Member] Physical Commodities Inventory - Precious Metals Schedule of Expected Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Earnings Per Share [Abstract] Earnings Per Share [Abstract] Derivative Netting Adjustment [Axis] Derivative Netting Adjustment [Axis] Derivative Netting Axis. Repurchase Agreements and Similar Transactions, Maturity Periods [Axis] Repurchase Agreements and Similar Transactions, Maturity Periods [Axis] Total property and equipment Property, Plant and Equipment, Gross Convertible senior notes Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt Allowance for doubtful accounts receivable Accounts Receivable, Allowance for Credit Loss Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent Crude Oil And Low Sulfur Fuel Oil Crude Oil And Low Sulfur Fuel Oil [Member] Crude Oil And Low Sulfur Fuel Oil Total revenues Total revenues Revenues Fair value of securities received as collateral that can be resold or repledged Fair Value of Securities Received as Collateral that Can be Resold or Repledged Net increase in provision for bad debts Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease) Schedule of Derivative Instruments Included in Trading Activities Schedule of Derivative Instruments Included in Trading Activities [Table Text Block] Weighted average  exercise price, Beginning (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Asset Acquisition [Domain] Asset Acquisition [Domain] Europe Europe [Member] Defined benefit plan, plan assets, amount Defined Benefit Plan, Plan Assets, Amount Weighted Average Grant Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Other Other Sales Based Commissions [Member] Other Sales Based Commissions [Member] Income tax rate change Effective Income Tax Rate Reconciliation, Percent Loss contingency, range of possible loss, portion not accrued Loss Contingency, Estimate of Possible Loss Receivable from clients, net (including $2.6 million and $1.5 million at fair value at September 30, 2021 and 2020, respectively) Receivables from Customers United States UNITED STATES Securities purchased under agreements to resell, gross Securities Purchased under Agreements to Resell, Gross Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract] Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract] Leases [Abstract] Income Taxes Income Tax, Policy [Policy Text Block] Insurance and annuity products Insurance Annuity Trailing Commissions [Member] Insurance Annuity Trailing Commissions Identifiable intangible assets Finite-Lived Intangible Assets, Remaining Amortization Period Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Qualified Plan Qualified Plan [Member] Total compensation and other expenses Noninterest Expense Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Purchase obligation, due in next twelve months Purchase Obligation, to be Paid, Year One Net contribution: Net Segment Contribution Net segment contribution equals revenues less cost of sales, transaction-based clearing expenses, variable bonus compensation, introducing broker commissions and interest expense. Diluted (in shares) Diluted shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted U.S. Income (Loss) from Continuing Operations before Income Taxes, Domestic Securities sold under agreements to repurchase Securities sold under agreements to repurchase Securities Sold under Agreements to Repurchase Insurance recoveries Insurance Recoveries Income Taxes Income Tax Disclosure [Text Block] OTC derivative brokerage OTC Derivative Brokerage [Member] OTC Derivative Brokerage [Member] Number of credit facilities scheduled to expire within one year Number Of Credit Facilities Scheduled To Expire Within One Year Number Of Credit Facilities Scheduled To Expire Within One Year South America South America [Member] Assets acquired Noncash or Part Noncash Acquisition, Value of Assets Acquired Share-based Compensation, Stock Options, Activity Share-based Payment Arrangement, Option, Activity [Table Text Block] Point-in-time Transferred at Point in Time [Member] Debt instrument, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Termination period Lessee, Operating Lease, Termination Period Lessee, Operating Lease, Termination Period Capital and Other Regulatory Requirements [Line Items] Capital and Other Regulatory Requirements [Line Items] Capital and Other Regulatory Requirements [Line Items] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Occupancy and equipment rental Occupancy, Net Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Credit Facility [Axis] Credit Facility [Axis] Income taxes payable Accrued Income Taxes Less: accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Consolidation Consolidation, Policy [Policy Text Block] Description of Business and Significant Accounting Policies Business Description and Accounting Policies [Text Block] Average expected life Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Eliminations Intersegment Eliminations [Member] Deposits and Receivables from Exchange Clearing Organizations [Domain] Deposits and Receivables from Exchange Clearing Organizations [Domain] Deposits and Receivables from Exchange Clearing Organizations Required net capital under commodity exchange act Minimum Requirement Futures Commission Merchant, Commodity Exchange Act, Required Net Capital Purchase Price Allocation Net assets acquired based on fair values: Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net [Abstract] Exchange-traded foreign exchange derivatives Foreign exchange Foreign Exchange Forward [Member] Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block] Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net Receivables from Clearing Organizations Money market mutual funds Money Market Funds [Member] Financial instruments sold, not yet purchased, at fair value Increase (Decrease) in Financial Instruments Sold, Not yet Purchased Cash and cash equivalents Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Loss Contingencies [Table] Loss Contingencies [Table] Revenue from contract with customer Revenue from Contract with Customer, Including Assessed Tax Defined contribution plan, employer matching contribution, percent of employees' gross pay Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Middle East and Asia Asia [Member] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Debt instrument, unamortized discount (premium) and debt issuance costs, net Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Nonqualified Plan Nonqualified Plan [Member] Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments, Gain (Loss) [Table] Title of 12(b) Security Title of 12(b) Security Accounts payable and other accrued liabilities (including contingent liabilities) [Axis] Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Axis] Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Axis] Statement [Table] Statement [Table] Shares Available for Grant Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward] Accounting Standards Adopted New Accounting Pronouncements, Policy [Policy Text Block] Other Deferred Tax Assets, Other Defined benefit plan, expected future benefit payment, year five Defined Benefit Plan, Expected Future Benefit Payment, Year Five Deposits and Receivables from Exchange Clearing Organizations [Axis] Deposits and Receivables from Exchange Clearing Organizations [Axis] Deposits and Receivables from Exchange Clearing Organizations Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Range [Axis] Statistical Measurement [Axis] Receivable from and Payable to Clients Accounts Receivable [Policy Text Block] Subsequent Event Subsequent Event [Member] Cover [Abstract] Deposits with and receivables from broker-dealers, clearing organizations, and counterparties Increase (Decrease) in Receivables from Brokers-Dealers and Clearing Organizations Finite-lived intangible assets, net amount Finite-Lived Intangible Assets, Net Goodwill Purchase price allocated to goodwill Goodwill Deferred payments on acquisitions Payments for (Proceeds from) Previous Acquisition Unrealized gain on securities Deferred Tax Liabilities, Unrealized Gains on Trading Securities Foreign earnings and losses taxed at different rates Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent Fiscal 2026 and thereafter Finite​ Lived ​Intangible ​Assets ​Amortization​ Expense ​After​ Year​ Four Finite​ Lived ​Intangible ​Assets ​Amortization​ Expense ​After​ Year​ Four Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition - restricted stock Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition - Restricted Stock Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days for restricted stock plan. Schedule of Goodwill Schedule of Goodwill [Table Text Block] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Operating lease costs Operating Lease, Cost Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Reserve Requirement [Axis] Reserve Requirement [Axis] Reserve Requirement [Axis] Pension Benefits Adjustment Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Inventory [Line Items] Inventory [Line Items] Product Financing Arrangements Product Financing Arrangements [Policy Text Block] Product Financing Arrangements [Policy Text Block] Defined contribution plan, maximum annual contributions per employee, percent Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent Total deferred taxes Total deferred taxes Deferred Income Tax Expense (Benefit) Carrying value Senior Secured Notes Senior Notes Senior Notes Due Twenty Twenty Five Senior Notes Due Twenty Twenty Five [Member] Senior Notes Due Twenty Twenty Five Condensed Cash Flow Statements, Captions [Line Items] Condensed Cash Flow Statements, Captions [Line Items] Number of credit facilities Number Of Credit Facilities Number of credit facilities available to the company. Cash and Cash Equivalents Cash and Cash Equivalents, Unrestricted Cash and Cash Equivalents, Policy [Policy Text Block] Deferred income taxes, net Deferred income taxes Deferred tax assets, net Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Debt Instrument, Description of Variable Rate Basis [Domain] Debt Instrument, Description of Variable Rate Basis [Domain] [Domain] for Debt Instrument, Description of Variable Rate Basis [Axis] Asset Acquisition [Axis] Asset Acquisition [Axis] Mutual funds Mutual Fund Sales Based Commissions [Member] Mutual Fund Sales Based Commissions [Member] Changes in operating assets and liabilities, net: Increase (Decrease) in Other Operating Assets and Liabilities, Net [Abstract] Federal statutory rate effect of: Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Asset management fees Asset Management [Member] Net change in lenders under loans with maturities 90 days or less Proceeds from (Repayments of) Short-term Debt, Maturing in Three Months or Less Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Net income Net income Net income Net Income (Loss) Attributable to Parent Entity Emerging Growth Company Entity Emerging Growth Company Precious metals retail sales Precious Metals Retail Sales [Member] Precious Metals Retail Sales Operating right of use assets Operating Lease, Right-of-Use Asset Net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards $0 - $5.00 Exercise Price Range One [Member] Exercise Price Range One [Member] Fillmore Advisors, LLC Fillmore Advisors, LLC [Member] Fillmore Advisors, LLC [Member] OTC interest rate derivatives Interest rate, equities, and indices Interest Rate Contract [Member] Income Statement Location [Axis] Income Statement Location [Axis] Condensed Financial Information of Parent Company Only Disclosure Condensed Financial Information of Parent Company Only Disclosure [Text Block] Finite-lived intangible assets, accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Range [Domain] Statistical Measurement [Domain] Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two OTC equity and indices derivatives OTC Equity And Indices Contract [Member] OTC Equity And Indices Contract Securities purchased under agreements to resell Increase (Decrease) in Receivables under Repurchase Agreements StoneX Financial StoneX Financial [Member] StoneX Financial U.S. bargain purchase gain Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent Broker-dealer, minimum net capital required, dividend withdrawal threshold, percent Broker-Dealer, Minimum Net Capital Required, Parent, Dividend Withdrawal Threshold, Percent Broker-Dealer, Minimum Net Capital Required, Parent, Dividend Withdrawal Threshold, Percent Sale of property and equipment Proceeds from Sale of Property, Plant, and Equipment Revenue from Contract with Customer [Abstract] Entity Filer Category Entity Filer Category FMS Sub-note commodity line of credit facility FMS Sub-Note Commodity Line Of Credit Facility [Member] FMS Sub-note commodity line of credit facility Business Segments [Axis] Segments [Axis] PAB Reserve Requirement PAB Reserve Requirement [Member] PAB Reserve Requirement [Member] Transaction-based clearing expenses Clearing and related expenses Floor Brokerage, Exchange and Clearance Fees Expected dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Payable to clients Increase (Decrease) in Payables to Customers Retirement Benefits [Abstract] Retirement Benefits [Abstract] Adjusted net capital of percentage Broker-Dealer, Minimum Net Capital Required, Parent, Aggregate Indebtedness Standard Debt instrument, redemption price, percentage Debt Instrument, Redemption Price, Percentage Share-based compensation APIC, Share-based Payment Arrangement, Increase for Cost Recognition Federal operating loss carryforwards, net of valuation allowances Federal operating loss carryforwards, net of valuation allowances Domestic operating loss carryforwards, net of valuation allowances Gain on acquisition Bargain purchase gain Business Combination, Bargain Purchase, Gain Recognized, Amount Total fair value of tangible assets acquired Total fair value of tangible assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Tangible Assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Tangible Assets Global Payments Global Payments Segment [Member] Global Payments Segment Total net assets acquired Noncash or Part Noncash Acquisition, Net Nonmonetary Assets Acquired (Liabilities Assumed) Preferred stock, $0.01 par value. Authorized 1,000,000 shares; no shares issued or outstanding Preferred Stock, Value, Outstanding Foreign earnings repatriated Foreign Earnings Repatriated Building Building [Member] Net income (loss) post-acquisition results of the acquired business Net income (loss) post-acquisition results of the acquired business Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual Weighted Average Grant Date Fair Value, Granted (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Net capital under commodity exchange act computation Actual Futures Commission Merchant, Commodity Exchange Act, Adjusted Net Capital Financial instruments owned and pledged as collateral, amount eligible to be repledged by counterparty Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty Exercise Price Range [Axis] Exercise Price Range [Axis] Other Other Commission And Clearing Fees [Member] Other Commission And Clearing Fees Credit Facility [Domain] Credit Facility [Domain] ASSETS Assets [Abstract] Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk Derivative Instruments and Hedging Activities Disclosure [Text Block] Number of Shares Outstanding, Granted Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Percentage of operating revenues Concentration Risk, Percentage Property and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Senior secured bridge loan Senior Secured Bridge Loan Senior Secured Bridge Loan Number of options outstanding, Beginning (in shares) Number of options outstanding, Ending (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Timing of Transfer of Good or Service [Axis] Timing of Transfer of Good or Service [Axis] Entity Address, City or Town Entity Address, City or Town Cash, securities and other assets segregated under federal and other regulations (including $14.1 million and $2.6 million at fair value at September 30, 2021 and 2020, respectively) Cash and securities segregated under federal and other regulations Cash and Securities Segregated under Federal and Other Regulations Defined benefit plan, assumptions used calculating benefit obligation, discount rate Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Trade/domain names Trade Names [Member] Debt Instrument [Axis] Debt Instrument [Axis] Other assets Increase (Decrease) in Prepaid Expense and Other Assets Other clearing related expenses Clearance Fees Less than 30 Days Maturity Less than 30 Days [Member] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Non-refundable commitment fee Non-Refundable Commitment Fee Non-Refundable Commitment Fee StoneX Financial Inc. Uncommitted Commodities Delivery Line StoneX Financial Inc. Uncommitted Commodities Delivery Line [Member] StoneX Financial Inc. Uncommitted Commodities Delivery Line Inventory, Current [Table] Inventory, Current [Table] Exchange-traded interest rate derivatives Exchange-traded interest rate contracts [Member] Exchange-traded interest rate contracts [Member] Physical commodities inventory Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory Right-of-use assets obtained in exchange for operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Schedule of Business Acquisition Pro Forma Financial Information Business Acquisition, Pro Forma Information [Table Text Block] Schedule of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Net income allocated to common stockholders Income from continuing operations allocated to common shareholders Income from continuing operations allocated to common shareholders represents income from continuing operations attributable to shareholders less allocation to participating securities plus interest on convertible debt less the allocation of the earnings from the interest on convertible debt to participating securities. Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Entity Interactive Data Current Entity Interactive Data Current Payables to clients - Derivatives Accounts Payable, Fair Value Disclosure Indefinite-lived Intangible Assets, Major Class Name [Domain] Indefinite-lived Intangible Assets, Major Class Name [Domain] Deposits and Receivables from Exchange Clearing Organizations Deposits and Receivables from Exchange Clearing Organizations [Member] Deposits and Receivables from Exchange Clearing Organizations [Member] Identified intangible assets and goodwill on acquisitions Goodwill and intangible assets acquired during the period Goodwill and intangible assets acquired during the period 2024 Lessee, Operating Lease, Liability, to be Paid, Year Three Physical commodities inventory at fair value Precious metals - held by broker -dealer subsidiary Physical commodities inventory at fair value Physical commodities inventory at fair value - precious metals Fair value of identifiable net assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Other Other (geographic location) [Member] Other (geographic location) [Member] Number of Shares Outstanding Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Insurance and annuity products Variable Annuity [Member] Identifiable intangible assets acquired Client relationships Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles Maximum amount of individual accounts receivable account Loss Contingency, Individual Accounts Maximum, Receivable Loss Contingency, Individual Accounts Maximum, Receivable Tax credit carryforwards Deferred Tax Assets, Tax Credit Carryforwards Exchange firm common stock Exchange firm Common Stock [Member] Exchange firm Common Stock [Member] Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Gross amount of secured financing Gross amount of secured financing Collateralized Financings Cash paid for amounts included in the measurement of operating lease liabilities Operating Lease, Payments Percentage of contingent earn-out payments Business Combination, Contingent Earn-out Payments, Percentage Of Segment Income Business Combination, Contingent Earn-out Payments, Percentage Of Segment Income Allowance for doubtful accounts receivable, recoveries Accounts Receivable, Allowance for Credit Loss, Recovery Impairment Exploration Abandonment and Impairment Expense Total merger consideration Total merger consideration Purchase price Business Combination, Consideration Transferred Provision for bad debts, net of recoveries and impairment Accounts Receivable, Credit Loss Expense (Reversal) Debt Instrument, Description of Variable Rate Basis [Axis] Debt Instrument, Description of Variable Rate Basis [Axis] Debt Instrument, Description of Variable Rate Basis [Axis] Long-term debt, gross Long-term Debt, Gross Total trailing commission Trailing Commissions [Member] Trailing Commissions [Member] Inventory adjustments Inventory Adjustments Total assets at fair value Assets, Fair Value Disclosure Document Transition Report Document Transition Report Capitalized software development Software Development [Member] Total liabilities and stockholders' equity Liabilities and Equity GILTI Effective Income Tax Rate Reconciliation, Other Adjustments, Percent 2026 Lessee, Operating Lease, Liability, to be Paid, Year Five Payables to Broker-dealers, Clearing Organizations and Counterparties [Axis] Payables to Broker-dealers, Clearing Organizations and Counterparties [Axis] Payables to Broker-dealers, Clearing Organizations and Counterparties [Axis] Weighted average  exercise price, exercised (in dollar per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Stock Option Activity, Additional Disclosures Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] U.S. government agency obligations U.S. government agency obligations US Government Agencies Debt Securities [Member] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Property, Plant and Equipment, Net [Abstract] OTC commodity derivatives Over the Counter (OTC) Commodity Contracts [Member] Over the Counter (OTC) Commodity Contracts [Member] Timing of Transfer of Good or Service [Domain] Timing of Transfer of Good or Service [Domain] Earnings per Share Earnings Per Share [Text Block] GMP Securities Acquisition GMP Securities Acquisition [Member] GMP Securities Acquisition [Member] Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Defined benefit plan, expected future benefit payment, year two Defined Benefit Plan, Expected Future Benefit Payment, Year Two Minimum Minimum [Member] Tellimer Tellimer [Member] Tellimer [Member] Operating revenues Operating revenues: Gross Profit 2023 Lessee, Operating Lease, Liability, to be Paid, Year Two Effect of exchange rates on cash, segregated cash, cash equivalents, and segregated cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Lenders under loans Payable to lenders under loans Long-term Line of Credit Schedule of Revenues from External Customers and Long-Lived Assets [Table] Schedule of Revenues from External Customers and Long-Lived Assets [Table] Fair value of securities received as collateral that have been resold or repledged Fair Value of Securities Received as Collateral that Have Been Resold or Repledged Liabilities, fair value disclosure Financial and Nonfinancial Liabilities, Fair Value Disclosure Income before tax Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets [Axis] Issuance of note payable Proceeds from Notes Payable Reclassifications Reclassification, Comparability Adjustment [Policy Text Block] Preferred stock - authorized (in shares) Preferred Stock, Shares Authorized Accounts payable and other accrued liabilities at fair value Accounts payable and other accrued liabilities - contingent consideration, fair value Accounts payable and other accrued liabilities - contingent consideration, fair value Business acquisition, cost incurred related to merger Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed Transaction-Based Clearing Expenses Floor Brokerage, Policy [Policy Text Block] Cumulative Effect, Period of Adoption [Axis] Cumulative Effect, Period of Adoption [Axis] Cash reserve deposit required Cash Reserve Deposit Required cashreservedepositrequired Agricultural related inventory Agricultural Related Inventory, Volume, Amount Agricultural Related Inventory, Volume, Amount Gain on stock sales of clearing organization memberships Gain (Loss) On Stock Sales Of Clearing Organizations Memberships Gain (Loss) On Stock Sales Of Clearing Organizations Memberships Percentage of stock purchased Business Acquisition, Percentage of Voting Interests Acquired Operating lease liabilities Increase (Decrease) In Operating Lease Liabilities Increase (Decrease) In Operating Lease Liabilities Equities and fixed income Equities and Fixed Income Commissions [Member] Equities and Fixed Income Commissions [Member] Cash paid for acquisitions Payments to Acquire Businesses, Net of Cash Acquired Foreign Currency Translation Adjustment Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Credit Facilities Debt Disclosure [Text Block] Schedule of Components of Income Tax Expense (Benefit) Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Intangible assets Deferred Tax Assets, Goodwill and Intangible Assets Share-Based Compensation Share-based Payment Arrangement [Text Block] Senior Notes Senior Notes [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Weighted average grant date fair value, expired (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Expired in Period, Weighted Average Grant Date Fair Value The weighted average grant-date fair value of options expired during the reporting period as calculated by applying the disclosed option pricing methodology. Finite-lived trade/domain names, gross amount Finite-Lived Trade Names, Gross Financial instruments owned, at fair value Increase (Decrease) in Financial Instruments Used in Operating Activities OTC foreign exchange derivatives Over the Counter (OTC) Foreign Exchange Contracts [Member] Over the Counter (OTC) Foreign Exchange Contracts [Member] Website domains Internet Domain Names [Member] Deposits with and Receivables from Broker-dealers, Clearing Organizations and Counterparties, and Payables to Broker-dealers, Clearing Organizations and Counterparties Due to and from Broker-Dealers and Clearing Organizations Disclosure [Text Block] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Gain Capital Group, LLC Gain Capital Group [Member] Gain Capital Group Business Acquisition, Pro Forma Information [Abstract] Business Acquisition, Pro Forma Information [Abstract] Additional goodwill Goodwill, Acquired During Period Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Office supplies and printing Supplies and Postage Expense Commitments and contingencies (Note 13) Commitments and Contingencies Goodwill and intangible assets, net Goodwill and intangible assets, net Amount combines the carrying amounts for goodwill and finite- and indefinite-lived intangible assets. Goodwill represents the carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquire, adjusted for any amortization recognized prior to adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions. Indefinite-lived intangible assets represent the carrying amount of intangible assets, excluding goodwill, which have a projected indefinite period of benefit (hence are not amortized), allocated to the reportable segment. These assets, acquired either individually or as part of a group of assets, in either an asset acquisition or business combination, are assessed at least annually for impairment. Examples may include trade secrets, contractual rights, trade names, and licensing agreements. Finite-lived intangible assets are the aggregate sum of gross carrying value of a major finite-lived intangible asset class, less accumulated amortization and any impairment charges. A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company. Accumulated other comprehensive loss, net Accumulated Other Comprehensive Income (Loss), Net of Tax Repurchase Agreements and Similar Transactions, Maturity Periods [Domain] Repurchase Agreements and Similar Transactions, Maturity Periods [Domain] Senior secured borrowings, net Loans Payable Debt issuance costs Payments of Debt Issuance Costs Receivables [Abstract] Commodities warehouse receipts Commodities Warehouse Receipts Commodities Warehouse Receipts Dividends Payments Of Dividends, Operating Activities Payments Of Dividends, Operating Activities Document Period End Date Document Period End Date Pension liabilities adjustment Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax Term loan periodic payment Debt Instrument, Periodic Payment, Principal Cash and cash equivalents - deposits and receivables Cash and Cash Equivalents - Deposits and Receivables Cash and Cash Equivalents - Deposits and Receivables Income tax rate holiday Effective Income Tax Rate Reconciliation, Tax Holiday, Percent Cumulative Effect, Period of Adoption, Adjusted Balance Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Entity Registrant Name Entity Registrant Name Treasury stock - shares (in shares) Treasury Stock, Shares Lenders under loans Debt, Long-term and Short-term, Combined Amount Retail Retail Segment [Member] Retail Segment [Member] Taxes allocated to stockholders’ equity, related to pension liabilities Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax Less: interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount EncoreFx Ltd EncoreFx Ltd [Member] EncoreFx Ltd PAB PAB [Member] PAB Exotix Partners, LLP Exotix Partners, LLP [Member] Exotix Partners, LLP [Member] Payables to broker dealer at fair value Payables to b/ds and counterparties at fair value Payables to b/ds and counterparties at fair value Cash and cash equivalents Cash $10.00 - $15.00 Exercise Price Range Three [Member] Exercise Price Range Three [Member] Net change in lenders under loans Proceeds from (Repayments of) Debt Financial Instrument [Axis] Financial Instrument [Axis] Allowance for doubtful accounts - deposits with and receivables from broker-dealers, clearings organizations, and counterparties Allowance For Doubtful Accounts - Deposits with and Receivables from Broker-Dealers, Clearings Organizations, and Counterparties Allowance For Doubtful Accounts - Deposits with and Receivables from Broker-Dealers, Clearings Organizations, and Counterparties Institutional Segment Institutional Institutional Segment [Member] Institutional Segment [Member] Weighted average remaining term (in years) Share-based Payment Arrangement, Option, Exercise Price Range, Outstanding, Weighted Average Remaining Contractual Term Receivable From Clients, Net Receivable From Clients, Net [Member] Receivable From Clients, Net Sales of physical commodities Revenue Not from Contract with Customer Gain Capital Holdings Inc Gain Capital Holdings Inc [Member] Gain Capital Holdings Inc [Member] Common Stock Common Stock [Member] Non-U.S. Income (Loss) from Continuing Operations before Income Taxes, Foreign Debt instrument remaining outstanding Debt Instrument Remaining Outstanding Debt Instrument Remaining Outstanding Professional fees Professional Fees Defined contribution plan, employer discretionary contribution amount Defined Contribution Plan, Employer Discretionary Contribution Amount Schedule of Financial Instruments Owned and Pledged as Collateral Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block] Fiscal 2023 Finite-Lived Intangible Asset, Expected Amortization, Year Two Amortization of share-based compensation expense Share-based Payment Arrangement, Noncash Expense AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Inventory [Axis] Inventory [Axis] Introducing broker commissions Noninterest Expense Commission Expense Securities borrowed Securities borrowed Securities Borrowed Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Depreciation expense Depreciation Mutual funds and other Mutual Funds and Other [Member] Mutual Funds and Other [Member] Customer SRBA Customer SRBA [Member] Customer SRBA Allowance for Doubtful Accounts Allowance for Credit Losses [Text Block] Treasury Stock Treasury Stock [Member] Inventory, firm purchase commitment Inventory, Firm Purchase Commitment Inventory, Firm Purchase Commitment Purchase obligation, due after fifth year Purchase Obligation, to be Paid, after Year Five Schedule of Share-based Compensation, Restricted Stock Units Award Activity Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Impairment Asset Impairment Charges Payables to Broker-dealers, Clearing Organizations and Counterparties Payables to Broker-dealers, Clearing Organizations and Counterparties [Member] Payables to Broker-dealers, Clearing Organizations and Counterparties [Member] Pledged assets separately reported, securities Pledged for repurchase agreements, at fair value Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements Overnight and Open Maturity Overnight and on Demand [Member] Other assets Business ​Combination​, Recognized​ Identifiable​ Assets Acquired ​And ​Liabilities ​Assumed, ​Other​ Assets Business ​Combination​, Recognized​ Identifiable​ Assets Acquired ​And ​Liabilities ​Assumed, ​Other​ Assets Share-based compensation arrangement by share-based payment award, non-option equity instruments, granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted Purchase obligation, due in second and third year Purchase Obligation, to be Paid, Year Two and Three Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Derivative, fair value, net Derivative, Fair Value, Net Pension Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions Defined benefit plan contributions Defined Benefit Plan, Plan Assets, Contributions by Employer Line of credit facility, interest rate at period end Line of Credit Facility, Interest Rate at Period End U.S. Treasury obligations US Government Debt Securities [Member] Total liabilities Liabilities Financial Instruments Owned Financial instruments owned [Member] Financial instruments owned [Member] $50.00 - $55.00 Exercise Price Range Eleven [Member] Exercise Price Range Eleven [Member] Minimum regulatory requirement Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated Commerical Segment Commerical Segment [Member] Commerical Segment Fiscal 2022 Finite-Lived Intangible Asset, Expected Amortization, Year One Weighted average  exercise price, granted (in dollar per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Acquisition of businesses: Noncash or Part Noncash Acquisition, Net Nonmonetary Assets Acquired (Liabilities Assumed) [Abstract] Stock options expired in period (in shares) (in shares) Number of options outstanding, expired (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period Derivatives Derivative [Member] Consolidation Items [Axis] Consolidation Items [Axis] Operating loss carryforwards Operating Loss Carryforwards Common stock - issued (in shares) Common Stock, Shares, Issued Contingent Consideration Contingent Consideration [Member] Contingent 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. Preferred stock - issued (in shares) Preferred Stock, Shares Issued Reserve Requirement [Domain] Reserve Requirement [Domain] Reserve Requirement Domain names Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Capital and Other Regulatory Requirements [Table] Capital and Other Regulatory Requirements [Table] Capital and Other Regulatory Requirements [Table] Eurodollar Eurodollar [Member] Regulatory Requirements and Subsidiary Dividend Restrictions - Customer Reserve Requirements [Abstract] Regulatory Requirements and Subsidiary Dividend Restrictions - Customer Reserve Requirements [Abstract] Regulatory Requirements and Subsidiary Dividend Restrictions - Customer Reserve Requirements [Abstract] Summary of Changes in Accumulated Other Comprehensive Loss Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Exchange Memberships Representing an Ownership Interest Exchange memberships representing an ownership interest [Member] Exchange memberships representing an ownership interest [Member] Insurance General Insurance Expense Software Software and Software Development Costs [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Accumulated Other Comprehensive Loss, Net Comprehensive Income (Loss) Note [Text Block] Deposits and receivables from broker dealer at fair value Deposits and receivables from bds and counterparties at fair value Deposits and receivables from b/ds and counterparties at fair value Fair Value, Measurement Frequency [Domain] Measurement Frequency [Domain] Interest expense Interest Expense Business licenses Licensing Agreements Licensing Agreements [Member] Net assets denominated in argentine pesos Net Assets Denominated In Argentine Pesos Net Assets Denominated In Argentine Pesos Expected long-term return Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets UOB Bullion and Futures UOB Bullion and Futures [Member] UOB Bullion and Futures Non-trading technology and support Information Technology and Data Processing Securities loaned, gross Securities Loaned, Gross Purchase price Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net Over 90 Days Maturity Greater than 90 Days [Member] City Area Code City Area Code Defined benefit plan, expected future benefit payment, year one Defined Benefit Plan, Expected Future Benefit Payment, Year One Retained earnings Retained Earnings (Accumulated Deficit) Entity Public Float Entity Public Float Fair Value of exchange memberships Fair Value of Exchange Memberships Fair Value of Exchange Memberships Financial instruments owned and pledged as collateral, amount not eligible to be repledged by counterparty Financial Instruments Owned and Pledged as Collateral, Amount Not Eligible to be Repledged by Counterparty Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Risk free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance Derivative Instruments, Gain (Loss) [Table Text Block] Amendment Flag Amendment Flag Securities sold under agreements to repurchase, Offset Securities Sold under Agreements to Repurchase, Asset Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] Derivative, number of instruments held Derivative, Number of Instruments Held Other Expenses [Abstract] Other Expenses [Abstract] Receivables from clients at fair value Receivables From Customers, Fair Value Disclosure Receivables From Customers, Fair Value Disclosure Contingent consideration, net Accretion Expense Indefinite-lived intangible assets Indefinite-lived Intangible Assets (Excluding Goodwill) Exercise of stock options Proceeds from Stock Options Exercised Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] $5.00 - $10.00 Exercise Price Range Two [Member] Exercise Price Range Two [Member] Retained earnings, before tax Retained Earnings (Accumulated Deficit), Before Tax Retained Earnings (Accumulated Deficit), Before Tax Statement, Equity Components [Axis] Equity Components [Axis] Equity Components [Axis] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] Fair Value Disclosures [Abstract] Selling and marketing expense Selling and Marketing Expense [Member] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Defined benefit plan, plan assets, actual allocation, percentage Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage Weighted-average number of common shares outstanding: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Physical commodities inventory Inventory, Net Schedule of Segment Reporting Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Payables to Broker-dealers, Clearing Organizations and Counterparties [Domain] Payables to Broker-dealers, Clearing Organizations and Counterparties [Domain] Payables to Broker-dealers, Clearing Organizations and Counterparties Entity File Number Entity File Number Income Tax Disclosure - Tax Reform [Abstract] Income Tax Disclosure - Tax Reform [Abstract] Income Tax Disclosure - Tax Reform [Abstract] U.S. federal Deferred Federal Income Tax Expense (Benefit) Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] $30.00 - $35.00 Exercise Price Range Seven [Member] Exercise Price Range Seven [Member] Weighted average  exercise price, expired (in dollar per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price After 2026 Lessee, Operating Lease, Liability, to be Paid, after Year Five Other SEC Schedule, 12-09, Valuation Allowances and Reserves, Addition, Recovery Net change in total valuation allowance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Physical Commodities Inventory [Domain] Physical Commodities Inventory [Domain] Physical Commodities Inventory Product and Service [Axis] Product and Service [Axis] Number of accounts Number Of Accounts Number Of Accounts Other Expenses Other Income and Other Expense Disclosure [Text Block] Preferred stock - par value (in dollar per share) Preferred Stock, Par or Stated Value Per Share Percentage of net capital under commodity exchange act computation Futures Commission Merchant, Commodity Exchange Act, Adjusted Net Capital, Percent Of Retail Customer Liabilities Over Threshold Futures Commission Merchant, Commodity Exchange Act, Adjusted Net Capital, Percent Of Retail Customer Liabilities Over Threshold Selling and marketing Selling and Marketing Expense Share-based compensation arrangement by share-based payment award, shares issued in period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period $45.00 - $50.00 Exercise Price Range Ten [Member] Exercise Price Range Ten [Member] Payable to broker-dealers, clearing organizations, and counterparties Business ​Combination,​ Recognized ​Identifiable ​Assets Acquired ​And ​Liabilities​ Assumed​, Payable To Broker Dealer, Clearing Organizations, And Counterparties Business ​Combination,​ Recognized ​Identifiable ​Assets Acquired ​And ​Liabilities​ Assumed​, Payable To Broker Dealer, Clearing Organizations, And Counterparties Number of different types of foreign currencies (more than) Number of different types of foreign currencies Number of different types of foreign currencies the company trades Net costs not allocated to operating segments Costs not allocated to operating segments Costs not allocated to operating segments Gain on acquisitions and other gains Other Nonoperating Gains (Losses) State and local net operating loss carryforwards of net of valuation allowance Deferred Tax Assets, Net of Valuation Allowance, Operating Loss Carryforwards, State and Local Deferred Tax Assets, Net of Valuation Allowance, Operating Loss Carryforwards, State and Local - Amount after allocation of valuation allowances of deferred tax asset attributable to deductible state and local operating loss carryforwards. Statement [Line Items] Statement [Line Items] Long-term line of credit, noncurrent Long-term Line of Credit, Noncurrent Securities and Other Assets Segregated Under Federal and Other Regulations [Domain] Securities and Other Assets Segregated Under Federal and Other Regulations [Domain] Securities and Other Assets Segregated Under Federal and Other Regulations Recovery bad debt on physical coal Provision for Other Credit Losses Weighted Average  Exercise Price Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Debt Disclosure [Abstract] Entity Address, State or Province Entity Address, State or Province Compensation and other expenses: Non-interest expenses: Noninterest Expense [Abstract] Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] StoneX Markets LLC StoneX Markets LLC [Member] StoneX Markets LLC Valuation allowance Less valuation allowance Deferred Tax Assets, Valuation Allowance Corporate Unallocated Corporate, Non-Segment [Member] Entity [Domain] Entity [Domain] Line of credit facility Line of Credit, Current Other expense Other Expense [Member] Retirement Plans Retirement Benefits [Text Block] Segment income (loss): Segment Income Segment Income equals net contribution less non-variable direct segment costs. Stock options granted (in shares) Number of options outstanding, granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Entity Shell Company Entity Shell Company Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Asset Class [Axis] Asset Class [Axis] Local Phone Number Local Phone Number Deferred taxes: Deferred Federal, State and Local, Tax Expense (Benefit) [Abstract] Total assets Total assets: Assets Pension liability Deferred Tax Liabilities, Defined Pension Liability Deferred Tax Liabilities, Defined Pension Liability Gain (loss) related to litigation settlement Gain (Loss) Related to Litigation Settlement Plan Name [Domain] Plan Name [Domain] Sweep program fees Sweep Program Fees [Member] Sweep Program Fees [Member] Defined contribution plan, employers matching contribution, annual vesting percentage, two to three years Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, Two to Three Years Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, Two to Three Years Cash paid for interest Interest Paid, Excluding Capitalized Interest, Operating Activities Segment, Geographical [Domain] Geographical [Domain] Repayments of note payable Repayments of Notes Payable StoneX Group Parent Company [Member] U.S. permanent items Effective Income Tax Rate Reconciliation, Permanent Items, Percent Effective Income Tax Rate Reconciliation, Permanent Items, Percent Recovery of bad debt on physical coal Bad debt expense (recovery) Provision for Other Losses Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Derivative Contract Type [Domain] Derivative Contract [Domain] Agency mortgage-backed obligations Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] Cash Cash [Member] Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption [Domain] GIROXX GIROXX Acquisition [Member] GIROXX Acquisition [Member] Short-term debt Short-term Debt Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Schedule of Debt Schedule of Debt [Table Text Block] Carl Kliem S.A. Carl Kliem S.A. [Member] Carl Kliem S.A. [Member] Furniture and fixtures Furniture and Fixtures [Member] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Entity Tax Identification Number Entity Tax Identification Number Earnings per share: Earnings Per Share, Basic [Abstract] Non-deductible compensation Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent Collateralized transactions: Collateralized Agreements [Abstract] Basic (in shares) Common shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in dollar per share) Earnings Per Share, Diluted Segment [Domain] Segments [Domain] Amortization and extinguishment of debt issuance costs Amortization of Debt Issuance Costs and Discounts Advisory and consulting fees Advisory and Consulting Fees [Member] Advisory and Consulting Fees [Member] Total sales-based commission Sales Based Commissions [Member] Sales Based Commissions [Domain] Trading (losses)/gains, net Trading Gain (Loss) Indefinite-lived intangible assets acquired Indefinite-lived Intangible Assets Acquired Income taxes paid, net of cash refunds Income taxes paid/(received), net of cash refunds Income Taxes Paid, Net Investment in subsidiaries Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Leasehold improvements Leaseholds and Leasehold Improvements [Member] Accounting Standards Update [Extensible List] Accounting Standards Update [Extensible Enumeration] Total intangible assets, net amount Intangible Assets, Net (Excluding Goodwill) Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent 401k Plan 401k Plan [Member] 401k Plan [Member] Other comprehensive gain/(loss), net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Lenders Under Loans and Senior Secured Borrowings Debt, Policy [Policy Text Block] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Property and equipment, net Property and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Assets Sold under Agreements to Repurchase [Line Items] Assets Sold under Agreements to Repurchase [Line Items] Proceeds from lenders under loans with maturities greater than 90 days Proceeds from Short-term Debt, Maturing in More than Three Months Senior secured borrowings, net Senior secured borrowings, net Notes Payable Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Bad debt reserve Deferred Tax Asset, Tax Deferred Expense, Reserve and Accrual, Accounts Receivable, Allowance for Credit Loss Depreciation and amortization Depreciation, Depletion and Amortization Purchase price allocated to client base intangible assets acquired Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles Indefinite-lived license agreements Indefinite-Lived License Agreements Income tax rate change Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent Fair Value, Assets Measured on Recurring Basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Accumulated Other Comprehensive Loss, net Accumulated Other Comprehensive Loss, net AOCI Attributable to Parent [Member] Physical commodities inventory Increase (Decrease) in Inventories Other assets Other assets Other Assets Common stock - outstanding (in shares) Common stock outstanding (in shares) Common Stock, Shares, Outstanding Financial Instruments [Domain] Financial Instruments [Domain] Exchange and Clearing Organization Memberships Exchange Memberships, Policy [Policy Text Block] Brokers and Dealers [Abstract] Brokers and Dealers [Abstract] Income taxes receivable Income Taxes Receivable Investment in subsidiaries for equity method accounting Adjustment to Investment in Subs Revenue for Equity Method Accounting Adjustment to Investment in Subs Revenue for Equity Method Accounting Deferred tax assets: Deferred Tax Assets, Gross [Abstract] Shares Available for Grant, Granted Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Period Increase (Decrease) Maximum borrowing capacity under credit facilities Maximum Borrowing Capacity Under Credit Facilities Maximum Borrowing Capacity Under Credit Facilities Current taxes: Current Federal, State and Local, Tax Expense (Benefit) [Abstract] Exercise price range, upper range limit Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit Customer base Customer Relationships [Member] Introducing Broker Commissions Commissions Expense, Policy [Policy Text Block] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Foreign permanent items Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Percent Property and Equipment, net Property, Plant and Equipment Disclosure [Text Block] Derivative Netting [Domain] Derivative Netting [Domain] Derivative Netting Condensed Financial Information Disclosure [Abstract] Condensed Financial Information Disclosure [Abstract] Accounts Payable and Other Accrued Liabilities [Domain] Accounts Payable and Other Accrued Liabilities [Domain] Accounts Payable and Other Accrued Liabilities Defined benefit plan, benefit obligation Defined Benefit Plan, Benefit Obligation Capitalized software development Capitalized Computer Software, Gross Debt Instrument [Line Items] Debt Instrument [Line Items] Customer base Client Base Intangible Assets Customer-Related Intangible Assets [Member] Collateral that can be sold or repledged Securities Sold under Agreements to Repurchase, Fair Value of Collateral Total revenues Business Acquisition, Pro Forma Revenue Physical commodities inventory, net (including $359.9 million and $215.7 million at fair value at September 30, 2021 and 2020, respectively) Physical commodities inventory Inventory, Gross Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies Other deferred liabilities Deferred Tax Liabilities, Other Equipment Equipment [Member] Foreign operating loss carryforwards, net of valuation allowances Deferred Tax Assets, Net of Valuation Allowance, Operating Loss Carryforwards, Foreign Deferred Tax Assets, Net of Valuation Allowance, Operating Loss Carryforwards, Foreign Line of Credit Facility [Table] Line of Credit Facility [Table] Trade conversion fees Trade Conversion Fees [Member] Trade Conversion Fees [Domain] Payable to clients Business ​Combination, ​Recognized ​Identifiable ​Assets ​Acquired ​And​ Liabilities​ Assumed,​ Payable To Clients Business ​Combination, ​Recognized ​Identifiable ​Assets ​Acquired ​And​ Liabilities​ Assumed,​ Payable To Clients Payable to broker-dealers, clearing organizations and counterparties Increase (Decrease) in Payables to Broker-Dealers and Clearing Organizations Schedule of Goodwill [Table] Schedule of Goodwill [Table] Allocated share-based compensation expense Share-based Payment Arrangement, Expense Cost of Sales of Physical Commodities Cost of Goods and Service [Policy Text Block] Debt instrument offering price, percentage Debt Instrument, Discount Rate at Issuance of Face Value Debt Instrument, Discount Rate at Issuance of Face Value Clients (including $291.5 million and $(222.7) million at fair value at September 30, 2021 and 2020, respectively) Payable to clients Broker-Dealer, Payable to Customer Cash, securities and other assets segregated under federal and other regulations Business​ Combination, ​Recognized​ Identifiable​ Assets ​Acquired And Liabilities Assumed, Cash, Securities And Other Assets Segregated Business​ Combination ​Recognized​ Identifiable​ Assets ​Acquired​ And ​Liabilities ​Assumed​ Cash securities and other assets segregated Weighted average remaining term (in years), exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Non cash equivalent segregated assets Non cash equivalent segregated assets Non cash equivalent segregated assets Defined Contribution Plan Disclosure [Line Items] Defined Contribution Plan Disclosure [Line Items] Compensation and benefits Labor and Related Expense Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Investments [Domain] Investments [Domain] Soybeans Soybeans [Member] Soybeans Number of global financial markets Number Of Global Financial Markets Number Of Global Financial Markets Payables to: Payables and Accruals [Abstract] Total fair value of tangible liabilities assumed Liabilities assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Schedule of Income before Income Tax, Domestic and Foreign Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] 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 Cash, segregated cash, cash equivalents, and segregated cash equivalents at beginning of period Cash, segregated cash, cash equivalents, and segregated cash equivalents at end of period Total cash, segregated cash, cash equivalents, and segregated cash equivalents shown in the consolidated statements of cash flows Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Schedule of Derivative Instruments Schedule of Derivative Instruments [Table Text Block] 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 Common stock - par value (in dollar per share) Common Stock, Par or Stated Value Per Share Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Commodities leases Commodities Leases and Unpriced Positions [Member] Commodities Leases and Unpriced Positions [Member] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Finite-lived intangible assets, gross amount Finite-Lived Intangible Assets, Gross Receivables from clients Business Combination, Acquired Receivables, Gross Contractual Amount Entity Central Index Key Entity Central Index Key Security Exchange Name Security Exchange Name Cash and cash equivalents, fair value Cash and cash equivalents, fair value Cash and Cash Equivalents, Fair Value Disclosure Commodities warehouse receipts Commodities Warehouse Receipts [Member] Commodities Warehouse Receipts [Member] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] Exercise Price Range [Domain] Fair Value, Measurements, Recurring Fair Value, Recurring [Member] 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 Number of money transmitter licenses Number Of State Of Money Transmitter Licenses Number Of State Of Money Transmitter Licenses Current Fiscal Year End Date Current Fiscal Year End Date Accounts receivable, allowance for doubtful accounts Accounts Receivable, Allowance for Credit Loss, Writeoff 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 Financial instruments sold, not yet purchased, at fair value Financial instruments sold, not yet purchased, at fair value Financial Instruments Sold, Not yet Purchased, at Fair Value Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Derivative asset, notional amount Derivative Asset, Notional Amount Impairment charges Capitalized Computer Software, Impairments Weighted Average Grant Date Fair Value, Vested (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Coininvest and EPMT Acquisitions Coininvest and EPMT Acquisitions [Member] Coininvest and EPMT Acquisitions [Member] Income taxes receivable Increase (Decrease) in Income Taxes Receivable Aggregate cash consideration Payments to Acquire Businesses, Gross Communications Communication Defined Contribution Plan [Table] Defined Contribution Plan [Table] Line of credit facility borrowing Line of Credit Facility, Maximum Borrowing Capacity Goodwill, foreign currency translation gain (loss) Goodwill, Foreign Currency Translation Gain (Loss) Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Other international Other International [Member] Other International Other non-income taxes Taxes, Miscellaneous Payments for legal settlements Payments for Legal Settlements Amount outstanding Amount Outstanding on Committed Credit Facilities Amount Outstanding on Committed Credit Facilities Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Remeasurement losses Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain (Loss), Net Long-lived assets, as defined: Long-Lived Assets Asset-backed obligations Asset-backed obligations Asset-backed Securities [Member] Dilutive potential common shares outstanding: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Operating lease liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Operating Lease Liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Operating Lease Liability Payables To Clients Payables To Clients [Member] Payables To Clients Cost of sales of physical commodities Cost of Goods and Service, Excluding Depreciation, Depletion, and Amortization Weighted average grant date fair value, forfeited (in dollar per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeited in Period, Weighted Average Grant Date Fair Value The weighted average grant-date fair value of options forfeited during the reporting period as calculated by applying the disclosed option pricing methodology. StoneX Financial Pte. Ltd. StoneX Financial Pte. Ltd. [Member] StoneX Financial Pte. Ltd. Member Securities segregated and pledged to exchange-clearing organizations Securities Segregated under Other Regulations Derivative liability, fair value, gross liability Derivative Liability, Fair Value, Gross Liability Allowance for doubtful accounts Financing Receivable, Allowance for Credit Loss Cash segregated under federal and other regulations Cash Segregated under Commodity Exchange Act Regulation Client account fees Client Account Fees [Member] Client Account Fees [Member] Number of outstanding options (in share) Share-based Payment Arrangement, Option, Exercise Price Range, Shares Outstanding Balance, beginning of year Balance, end of year SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Exchange-traded equity index derivatives Equity Contract [Member] Periodic pension costs (included in compensation and benefits) Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax Physical Commodities Inventory Inventory, Policy [Policy Text Block] Foreign tax expense Current Foreign Tax Expense (Benefit) Adjusted net capital Broker-Dealer, Minimum Net Capital Required, Broker-Dealer Subsidiary, Aggregate Indebtedness Standard Self insurance reserve and dental claims Self Insurance Reserve Common stock, $0.01 par value. Authorized 30,000,000 shares; 22,431,233 issued and 19,823,910 outstanding at September 30, 2021 and 21,798,551 issued and 19,376,594 outstanding at September 30, 2020 Common Stock, Value, Outstanding Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Other Other Expenses Commission and clearing fees Total commission and clearing fees Commission and Clearing Fees [Member] Commission and Clearing Fees [Member] Accounting Standards Update 2018-02 [Member] Accounting Standards Update 2016-13 [Member]