Debt Instrument, Discount Rate at Issuance of Face Value

No definition available.

Name:	intl_DebtInstrumentDiscountRateAtIssuanceOfFaceValue
Namespace Prefix:	intl_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Period between issuance and maturity of debt instrument, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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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+ Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow for a borrowing supported by a written promise to pay an obligation.

+ References

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Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
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- Details

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- Details

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Balance Type:
Period Type:

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Balance Type:
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- Details

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Balance Type:
Period Type:

- Details

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Period Type:

Credit Facilities - Narrative (Details) - USD ($)			9 Months Ended
Credit Facilities - Narrative (Details) - USD ($)	Jun. 01, 2026	Dec. 01, 2025	Jun. 30, 2026	Jun. 30, 2025	May 31, 2026	Jul. 08, 2025	Mar. 01, 2024
Line of Credit Facility [Line Items]
Repayments of note payable		$ 6,300,000	$ 6,300,000	$ 0
StoneX Financial Inc. Subordinated Credit Facility \| Line of Credit
Line of Credit Facility [Line Items]
Total commitment			$ 155,000,000.0
Debt term	1 year
Subordinated Credit Facility \| Line of Credit \| R.J. O’Brien
Line of Credit Facility [Line Items]
Total commitment					$ 180,000,000.0
Senior Secured Notes due 2031 \| Senior Notes
Line of Credit Facility [Line Items]
Debt instrument, face amount							$ 550,000,000.0
Debt instrument, interest rate, stated percentage			7.875%				7.875%
Debt instrument offering price, percentage							100.00%
Debt issuance costs, gross							$ 7,700,000
Senior Secured Notes due 2032 \| Senior Notes
Line of Credit Facility [Line Items]
Debt instrument, face amount						$ 625,000,000.0
Debt instrument, interest rate, stated percentage			6.875%			6.875%
Debt instrument offering price, percentage						100.00%
Debt issuance costs, gross						$ 10,500,000
Revolving commitments \| Committed Credit Facilities
Line of Credit Facility [Line Items]
Total commitment			$ 1,760,000,000