v3.26.1
Revenue from Contracts with Clients - Schedule of Principal Gains, Net Related To Income and Expense of Dividends (Details) - Equity securities - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Disaggregation of Revenue [Line Items]        
Dividend (expense)/income, net reported within Principal gains, net $ (0.9) $ (2.0) $ (1.7) $ (0.7)
Dividend income on long equity positions        
Disaggregation of Revenue [Line Items]        
Dividend (expense)/income, net reported within Principal gains, net 46.0 35.8 116.9 108.7
Dividend expense on short equity positions        
Disaggregation of Revenue [Line Items]        
Dividend (expense)/income, net reported within Principal gains, net $ (46.9) $ (37.8) $ (118.6) $ (109.4)