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Regulatory Requirements and Subsidiary Dividend Restrictions - Narrative (Details) | 12 Months Ended
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Sep. 30, 2025 USD ($)
Capital and Other Regulatory Requirements [Line Items] |
Adjusted net capital | $ 10,000,000
StoneX Financial Inc. |
Capital and Other Regulatory Requirements [Line Items] |
Adjusted net capital | $ 1,500,000
Adjusted net capital of percentage (as a percent) | 8.00%
Broker-dealer, minimum net capital required, dividend withdrawal threshold, percent (as a percent) | 120.00%
Net capital under commodity exchange act computation | $ 519,100,000
Required net capital under commodity exchange act | 362,800,000
GAIN Capital Group, LLC |
Capital and Other Regulatory Requirements [Line Items] |
Net capital under commodity exchange act computation | 65,800,000
Required net capital under commodity exchange act | 30,400,000
GAIN Capital Group, LLC | Customer and Non-Customer Risk Maintenance Margin |
Capital and Other Regulatory Requirements [Line Items] |
Adjusted net capital | $ 1,000,000
Adjusted net capital of percentage (as a percent) | 8.00%
GAIN Capital Group, LLC | Retail Customer Liabilities |
Capital and Other Regulatory Requirements [Line Items] |
Net capital under commodity exchange act computation | $ 20,000,000
Percentage of net capital under commodity exchange act computation (as a percent) | 5.00%
GAIN Capital Group, LLC | Liabilities Owed to Counterparties |
Capital and Other Regulatory Requirements [Line Items] |
Required net capital under commodity exchange act | $ 10,000,000
Percentage of required net capital under commodity exchange act (as a percent) | 10.00%
R.J. O’Brien & Associates LLC |
Capital and Other Regulatory Requirements [Line Items] |
Net capital under commodity exchange act computation | $ 367,400,000
Required net capital under commodity exchange act | 275,800,000
R.J. O’Brien & Associates LLC | Customer and Non-Customer Risk Maintenance Margin |
Capital and Other Regulatory Requirements [Line Items] |
Adjusted net capital | $ 20,000,000
R.J. O’Brien & Associates LLC | Customer Risk Maintenance Margin |
Capital and Other Regulatory Requirements [Line Items] |
Adjusted net capital of percentage (as a percent) | 8.00%
R.J. O’Brien & Associates LLC | Non-customer Risk Maintenance Margin |
Capital and Other Regulatory Requirements [Line Items] |
Adjusted net capital of percentage (as a percent) | 8.00%
StoneX Markets LLC |
Capital and Other Regulatory Requirements [Line Items] |
Net capital under commodity exchange act computation | $ 252,500,000
Required net capital under commodity exchange act | 154,400,000
Minimum regulatory capital requirement | $ 20,000,000

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- Definition Broker-Dealer, Minimum Net Capital Required, Broker-Dealer Subsidiary, Aggregate Indebtedness Standard, Percentage + References No definition available. + Details
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- Definition Futures Commission Merchant, Commodity Exchange Act, Required Net Capital, Percent Of Liabilities Owed to Counterparties + References No definition available. + Details
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- Definition Minimum amount of net capital required to be maintained by broker-dealer subsidiary to engage in security transaction, calculated under Aggregate Indebtedness Standard. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name Rule 15c3-1 -Number 240 -Section 15c3-1 -Publisher SEC + Details
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- Definition Amount of adjusted net capital of futures commission merchant (FCM) per Commodity Futures Trading Commission's (CFTC) requirement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name CFTC Regulation -Number 1 -Section 17 -Paragraph c -Subparagraph (5) -Publisher CFTC + Details
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- Definition Amount of net capital required to be maintained by futures commission merchant (FCM) per Commodity Futures Trading Commission's (CFTC) requirement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name CFTC Regulation -Number 1 -Section 17 -Paragraph a -Subparagraph (1)(i) -Publisher CFTC + Details
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- Definition Amount of minimum total risk-based capital required for capital adequacy as defined by regulatory framework. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 505 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477270/942-505-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 505 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Publisher FASB -URI https://asc.fasb.org/1943274/2147477270/942-505-50-1B + Details
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