Regulatory Requirements and Subsidiary Dividend Restrictions - Minimum Regulatory Net Capital (Details)	Sep. 30, 2022 USD ($)
Capital and Other Regulatory Requirements [Abstract]
Adjusted net capital	$ 10,000,000
Capital and Other Regulatory Requirements [Line Items]
Actual	20,000,000
Minimum Requirement	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	402,400,000
Minimum Requirement	250,100,000
StoneX Financial Ltd.
Capital and Other Regulatory Requirements [Line Items]
Actual	399,800,000
Minimum Requirement	358,000,000.0
Gain Capital Group, LLC
Capital and Other Regulatory Requirements [Abstract]
Adjusted net capital	1,000,000
Capital and Other Regulatory Requirements [Line Items]
Actual	49,200,000
Minimum Requirement	28,400,000
StoneX Financial Pte. Ltd.
Capital and Other Regulatory Requirements [Line Items]
Actual	58,000,000.0
Minimum Requirement	13,200,000
StoneX Markets LLC
Capital and Other Regulatory Requirements [Line Items]
Actual	191,400,000
Minimum Requirement	$ 128,800,000