Regulatory Requirements and Subsidiary Dividend Restrictions - Minimum Regulatory Net Capital (Details)	Sep. 30, 2023 USD ($)
Capital and Other Regulatory Requirements [Abstract]
Adjusted net capital	$ 10,000,000
StoneX Financial Inc.
Capital and Other Regulatory Requirements [Abstract]
Adjusted net capital	1,500,000
Capital and Other Regulatory Requirements [Line Items]
Actual	353,000,000.0
Minimum Requirement	220,500,000
StoneX Financial Ltd.
Capital and Other Regulatory Requirements [Line Items]
Actual	458,500,000
Minimum Requirement	358,000,000.0
Gain Capital Group, LLC
Capital and Other Regulatory Requirements [Line Items]
Actual	50,100,000
Minimum Requirement	29,300,000
StoneX Financial Pte. Ltd.
Capital and Other Regulatory Requirements [Line Items]
Actual	76,500,000
Minimum Requirement	24,400,000
StoneX Markets LLC
Capital and Other Regulatory Requirements [Line Items]
Actual	221,300,000
Minimum Requirement	$ 122,100,000