Credit Facilities - Credit Facilities and Financing Bridge Commitment (Details)	12 Months Ended
Sep. 30, 2023 USD ($) lender	Sep. 30, 2022 USD ($)
Line of Credit Facility [Line Items]
Uncommitted Credit Facilities	$ 55,500,000	$ 0
Notes payable to bank	7,500,000	8,100,000
Senior Secured Notes	342,100,000	339,100,000
Lenders under loans	$ 683,100,000	824,200,000
Notes payable to bank
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	2.35%
Senior Secured Notes
Line of Credit Facility [Line Items]
Interest rate percentage	8.625%
Debt instrument, unamortized discount (premium) and debt issuance costs, net	$ 5,800,000
Senior StoneX Group Inc. Committed Credit Facility \| Secured Debt
Line of Credit Facility [Line Items]
Line of credit facility borrowing	$ 42,500,000
Debt instrument, number of lenders \| lender	1
Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facilities	$ 1,200,000,000
Amount outstanding	278,000,000.0	477,000,000.0
Revolving Credit Facility \| Senior StoneX Group Inc. Committed Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility borrowing	500,000,000.0
Long-term line of credit, noncurrent	$ 150,000,000.0	260,000,000.0
Revolving Credit Facility \| Senior StoneX Group Inc. Committed Credit Facility \| Base Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	9.50%
Revolving Credit Facility \| Senior StoneX Group Inc. Committed Credit Facility \| SOFR
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	7.42%
Revolving Credit Facility \| StoneX Financial Inc.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	$ 190,000,000.0
Line of credit facility	$ 0	0
Interest rate percentage	8.00%
Revolving Credit Facility \| StoneX Commodity Solutions LLC
Line of Credit Facility [Line Items]
Line of credit facility borrowing	$ 400,000,000.0
Line of credit facility	$ 103,000,000.0	217,000,000.0
Revolving Credit Facility \| StoneX Commodity Solutions LLC \| Base Rate
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	8.50%
Revolving Credit Facility \| StoneX Commodity Solutions LLC \| SOFR
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate	7.69%
Revolving Credit Facility \| StoneX Financial Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	$ 100,000,000.0
Line of credit facility	$ 25,000,000.0	0
Interest rate percentage	7.81%
Revolving Credit Facility \| StoneX Financial Pte. Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	$ 10,000,000.0
Line of credit facility	$ 0	$ 0
Interest rate percentage	7.81%

Amount Outstanding on Committed Credit Facilities

No definition available.

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- Definition

Debt Instrument, Number of Lenders

+ References

No definition available.

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- Definition

Lines Of Credit Uncommitted Facilities

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No definition available.

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- Definition

Maximum Borrowing Capacity Under Credit Facilities

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No definition available.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

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- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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The carrying value as of the balance sheet date of the noncurrent portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

Including the current and noncurrent portions, the carrying value as of the balance sheet date of notes payable to banks, excluding mortgage notes, initially due beyond one year or beyond the operating cycle if longer.

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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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