v3.26.1
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Schedule of Net Gains/(Losses) from Derivative Contracts (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Derivative Instruments, Gain (Loss) [Line Items]        
Net gains from derivative contracts $ 69.2 $ 184.5 $ 373.3 $ 506.3
Commodities        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gains from derivative contracts 50.8 89.2 262.6 275.2
Foreign exchange        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gains from derivative contracts 11.7 39.3 48.4 106.4
Interest rate, equities, and indices        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gains from derivative contracts 22.7 33.5 74.1 83.4
To be announced and forward settling securities        
Derivative Instruments, Gain (Loss) [Line Items]        
Net gains from derivative contracts $ (16.0) $ 22.5 $ (11.8) $ 41.3