Condensed Financial Information of Parent Company Only Disclosure - Condensed Balance Sheets (Share Information) (Details) - $ / shares	Sep. 30, 2023	Sep. 30, 2022
Condensed Balance Sheet Statements, Captions [Line Items]
Preferred stock, par value (in dollar per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	1,000,000	1,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollar per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	200,000,000	200,000,000
Common stock, issued (in shares)	23,403,960	22,911,227
Common stock, outstanding (in shares)	20,796,637	20,303,904
Treasury stock, shares (in shares)	2,607,323	2,607,323
StoneX Group
Condensed Balance Sheet Statements, Captions [Line Items]
Preferred stock, par value (in dollar per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	1,000,000	1,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollar per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	200,000,000	200,000,000
Common stock, issued (in shares)	23,403,960	22,911,227
Common stock, outstanding (in shares)	20,796,637	20,303,904
Treasury stock, shares (in shares)	2,607,323	2,607,323