Amount Outstanding on Committed Credit Facilities

No definition available.

Name:	intl_AmountOutstandingOnCommittedCreditFacilities
Namespace Prefix:	intl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum Borrowing Capacity Under Credit Facilities

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

+ Details

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

- Definition

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

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+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- 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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+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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.

+ References

No definition available.

+ Details

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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.

+ References

+ Details

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

- 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.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, aggregate carrying value as of the balance sheet date of loans payable (with maturities initially due after one year or beyond the operating cycle if longer).

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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

- Definition

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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+ Details

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

- 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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Balance Type:	credit
Period Type:	instant

- 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.

+ References

+ Details

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

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=intl_FCSMarginLineOfCreditFacilityMember
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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=intl_StoneXLtdMember
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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=intl_IFFIUncommittedLinesOfCreditMember
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Credit Facilities - Credit Facilities and Financing Bridge Commitment (Details) - USD ($)	Sep. 30, 2022	Jul. 28, 2022	Jul. 27, 2022	Mar. 31, 2022	Sep. 30, 2021	Dec. 31, 2020
Line of Credit Facility [Line Items]
Payable to lenders under loans	$ 485,100,000				$ 248,600,000
Notes payable to bank	8,100,000				8,600,000	$ 9,000,000
Senior Secured Notes	339,100,000				336,900,000
Lenders under loans	824,200,000				755,600,000
Debt instrument, unamortized discount (premium) and debt issuance costs, net	8,800,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facilities	1,000,000,000
Amount outstanding	477,000,000.0				385,100,000
Revolving Credit Facility \| StoneX Inc. Bank of America Syndicated Credit Facility
Line of Credit Facility [Line Items]
Long-term debt, gross	0
Line of credit facility borrowing	475,000,000.0			$ 236,100,000
Maximum borrowing capacity under credit facilities	475,000,000.0
Senior secured borrowings, net	0				170,100,000
Long-term line of credit, noncurrent	260,000,000.0				0
Long-term debt	260,000,000.0				170,100,000
Revolving Credit Facility \| StoneX Financial Margin line of credit facility
Line of Credit Facility [Line Items]
Line of credit facility borrowing	75,000,000.0
Line of credit facility	0				0
Payable to lenders under loans	0				0
Revolving Credit Facility \| FMS Sub-note commodity line of credit facility
Line of Credit Facility [Line Items]
Line of credit facility borrowing	400,000,000.0	$ 400,000,000	$ 325,000,000
Line of credit facility	217,000,000.0				215,000,000.0
Revolving Credit Facility \| StoneX Financial Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	50,000,000
Line of credit facility	0				0
Revolving Credit Facility \| IFFI Uncommitted Lines of Credit
Line of Credit Facility [Line Items]
Line of credit facility borrowing	100,000,000
Payable to lenders under loans	0				0
Revolving Credit Facility \| Rabobank Uncommited Line of Credit
Line of Credit Facility [Line Items]
Short-term debt	$ 0				$ 25,000,000.0