Credit Facilities - Schedule of Debt (Details) - USD ($)	Dec. 31, 2024	Sep. 30, 2024
Line of Credit Facility [Line Items]
Lenders under loans	$ 550,000,000.0	$ 338,800,000
Uncommitted Credit Facilities	131,200,000	104,900,000
Note Payable to Bank	6,800,000	6,900,000
Total outstanding borrowings	1,093,300,000	881,900,000
Senior Secured Notes due 2031
Line of Credit Facility [Line Items]
Senior Secured Notes due 2031	543,300,000	543,100,000
Senior Secured Notes due 2031 \| Senior Notes
Line of Credit Facility [Line Items]
Debt instrument, unamortized discount (premium) and debt issuance costs, net	6,700,000	6,900,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility borrowing	1,205,000,000
Lenders under loans	412,000,000.0	227,000,000.0
Revolving Credit Facility \| Senior StoneX Group Inc. Committed Credit Facility - Revolving Line of Credit
Line of Credit Facility [Line Items]
Line of credit facility borrowing	500,000,000.0
Lenders under loans	274,000,000.0	161,000,000.0
Revolving Credit Facility \| StoneX Financial Inc.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	250,000,000.0
Lenders under loans	0	0
Revolving Credit Facility \| StoneX Commodity Solutions LLC
Line of Credit Facility [Line Items]
Line of credit facility borrowing	325,000,000.0
Lenders under loans	113,000,000.0	66,000,000.0
Revolving Credit Facility \| StoneX Financial Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	115,000,000.0
Lenders under loans	25,000,000.0	0
Revolving Credit Facility \| StoneX Financial Pte. Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	15,000,000.0
Lenders under loans	$ 0	$ 0

Lines Of Credit Uncommitted Facilities

No definition available.

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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

The carrying value as of the balance sheet date of the current and noncurrent portions 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

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

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.

+ References

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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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