Regulatory Requirements and Subsidiary Dividend Restrictions - Narrative (Details)	12 Months Ended
	Sep. 30, 2022 USD ($)
Capital and Other Regulatory Requirements [Line Items]
Adjusted net capital	$ 10,000,000
Net capital under commodity exchange act computation	20,000,000
Required net capital under commodity exchange act	10,000,000
StoneX Financial Inc.
Capital and Other Regulatory Requirements [Line Items]
Adjusted net capital	$ 1,500,000
Adjusted net capital of percentage	8.00%
Broker-dealer, minimum net capital required, dividend withdrawal threshold, percent	120.00%
Net capital under commodity exchange act computation	$ 402,400,000
Required net capital under commodity exchange act	250,100,000
Gain Capital Group, LLC
Capital and Other Regulatory Requirements [Line Items]
Adjusted net capital	$ 1,000,000
Adjusted net capital of percentage	8.00%
Net capital under commodity exchange act computation	$ 49,200,000
Percentage of net capital under commodity exchange act computation	5.00%
Required net capital under commodity exchange act	$ 28,400,000
Percentage of required net capital under commodity exchange act	10.00%