Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) $ in Millions	Sep. 30, 2023 USD ($)
StoneX Financial Inc.
Capital and Other Regulatory Requirements [Line Items]
Cash and securities segregated under commodity exchange act regulation	$ 6,166.2
Secured funds	261.0
Minimum regulatory requirement	6,091.9
Secured funds required under commodity exchange act	249.0
StoneX Financial Ltd.
Capital and Other Regulatory Requirements [Line Items]
Cash and securities segregated under commodity exchange act regulation	1,266.6
Minimum regulatory requirement	1,253.7
StoneX Financial Pte. Ltd.
Capital and Other Regulatory Requirements [Line Items]
Cash and securities segregated under commodity exchange act regulation	789.0
Minimum regulatory requirement	$ 772.4