Credit Facilities - Number of Credit Facilities (Details)	3 Months Ended
	Dec. 31, 2022 USD ($) facility	Dec. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)	Jul. 28, 2022 USD ($)	Apr. 21, 2022 USD ($)	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Number of credit facilities | facility	4
Maximum borrowing capacity under credit facilities	$ 1,105,000,000
Lenders under loans	582,300,000		$ 485,100,000
Notes payable to bank	$ 8,000,000.0		8,100,000			$ 9,000,000
Debt, weighted average interest rate						2.35%
Senior StoneX Group Inc. Committed Credit Facility - Revolving Line of Credit
Line of Credit Facility [Line Items]
Term of syndicated loan facility	3 years
Line of credit facility borrowing	$ 475,000,000.0
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility borrowing					$ 475,000,000
StoneX Financial Inc.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	180,000,000	$ 75,000,000
StoneX Commodity Solutions LLC
Line of Credit Facility [Line Items]
Line of credit facility borrowing	400,000,000.0			$ 400,000,000
StoneX Financial Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	50,000,000
Uncommitted Credit Facilities
Line of Credit Facility [Line Items]
Lenders under loans	$ 28,300,000		$ 0