Credit Facilities - Credit Facilities (Details)	Jun. 30, 2023 USD ($) facility	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Number of credit facilities | facility	4
Maximum borrowing capacity under credit facilities	$ 1,155,000,000
Notes payable to bank	7,600,000		$ 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]
Line of credit facility borrowing	500,000,000	$ 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
StoneX Financial Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	$ 75,000,000