v3.25.1
Credit Facilities - Credit Facilities and Financing Bridge Commitment (Details) - USD ($)
Mar. 31, 2025
Sep. 30, 2024
Line of Credit Facility [Line Items]    
Uncommitted Credit Facilities $ 97,200,000 $ 104,900,000
Note Payable to Bank 6,700,000 6,900,000
Total outstanding borrowings 884,500,000 881,900,000
Senior Secured Notes due 2031    
Line of Credit Facility [Line Items]    
Senior secured notes 543,600,000 543,100,000
Senior Secured Notes due 2031 | Senior Notes    
Line of Credit Facility [Line Items]    
Debt instrument, unamortized discount (premium) and debt issuance costs, net 6,400,000 6,900,000
Revolving Credit Facility    
Line of Credit Facility [Line Items]    
Maximum borrowing capacity under credit facilities 1,205,000,000  
Amount outstanding 237,000,000.0 227,000,000.0
Revolving Credit Facility | Senior StoneX Group Inc. Committed Credit Facility - Revolving Line of Credit    
Line of Credit Facility [Line Items]    
Line of credit facility borrowing 500,000,000.0  
Long-term line of credit, noncurrent 50,000,000.0 161,000,000.0
Revolving Credit Facility | StoneX Financial Inc.    
Line of Credit Facility [Line Items]    
Line of credit facility borrowing 250,000,000.0  
Line of credit facility 20,000,000.0 0
Revolving Credit Facility | StoneX Commodity Solutions LLC    
Line of Credit Facility [Line Items]    
Line of credit facility borrowing 325,000,000.0  
Line of credit facility 117,000,000.0 66,000,000.0
Revolving Credit Facility | StoneX Financial Ltd.    
Line of Credit Facility [Line Items]    
Line of credit facility borrowing 115,000,000.0  
Line of credit facility 50,000,000.0 0
Revolving Credit Facility | StoneX Financial Pte. Ltd.    
Line of Credit Facility [Line Items]    
Line of credit facility borrowing 15,000,000.0  
Line of credit facility $ 0 $ 0