v3.26.1
Segment Analysis - Schedule of Segment Reporting Information Examples (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Sep. 30, 2025
Segment Reporting [Line Items]          
Non-interest revenues $ 39,578.7 $ 34,386.1 $ 123,210.5 $ 98,444.9  
Interest income 614.3 442.7 1,773.3 1,209.9  
Total revenues 40,193.0 34,828.8 124,983.8 99,654.8  
Cost of sales of physical commodities 38,725.0 33,804.5 120,510.8 96,730.2  
Total operating revenues 1,468.0 1,024.3 4,473.0 2,924.6  
Transaction-based clearing expenses 144.3 94.9 429.6 273.2  
Introducing broker commissions 93.1 49.7 283.7 139.5  
Total interest expense 510.9 391.4 1,486.5 1,044.2  
Net operating revenues 719.7 488.3 2,273.2 1,467.7  
Variable compensation and benefits 244.0 143.9 708.4 423.9  
Net contribution 475.7 344.4 1,564.8 1,043.8  
Fixed compensation and benefits 149.8 123.4 448.5 363.0  
Trading systems and market information 25.7 21.3 76.5 60.8  
Professional fees 5.9 23.9 57.1 59.4  
Non-trading technology and support 30.1 21.1 85.1 61.7  
Selling and marketing 16.6 13.0 44.7 38.4  
Travel and business development 10.9 7.9 39.5 23.4  
Depreciation and amortization 26.9 14.9 78.8 46.2  
Bad debts, net of recoveries (1.0) 0.4 12.6 2.3  
Shared services 0.0 0.0 0.0 0.0  
Other fixed expenses 49.3 31.6 145.4 93.4  
Non-variable expenses 314.2 257.5 988.2 748.6  
Other gains (losses), net (1.7) (1.3) (4.8) 4.4  
Income before tax 159.8 85.6 571.8 299.6  
Total assets 54,046.0   54,046.0   $ 45,268.0
Operating Segments | Commercial          
Segment Reporting [Line Items]          
Non-interest revenues 39,084.3 33,990.9 121,669.5 97,301.8  
Interest income 92.9 42.9 258.5 142.3  
Total revenues 39,177.2 34,033.8 121,928.0 97,444.1  
Cost of sales of physical commodities 38,725.0 33,804.5 120,510.8 96,730.2  
Total operating revenues 452.2 229.3 1,417.2 713.9  
Transaction-based clearing expenses 36.5 21.5 108.7 58.2  
Introducing broker commissions 51.8 12.8 153.4 37.2  
Total interest expense 37.5 23.5 102.2 61.2  
Net operating revenues 326.4 171.5 1,052.9 557.3  
Variable compensation and benefits 80.6 44.5 256.8 141.6  
Net contribution 245.8 127.0 796.1 415.7  
Fixed compensation and benefits 24.4 19.9 71.4 56.8  
Trading systems and market information 5.3 4.4 15.5 13.1  
Professional fees 3.0 2.4 7.0 6.4  
Non-trading technology and support 1.2 0.4 2.3 1.2  
Selling and marketing 1.9 1.5 4.5 4.0  
Travel and business development 3.0 2.4 8.9 6.7  
Depreciation and amortization 5.7 2.0 17.3 5.9  
Bad debts, net of recoveries (1.3) 0.0 10.1 0.9  
Shared services 12.5 10.0 33.6 23.8  
Other fixed expenses 8.7 2.3 20.7 13.9  
Non-variable expenses 64.4 45.3 191.3 132.7  
Other gains (losses), net 0.0 1.0 0.0 1.0  
Income before tax 181.4 82.7 604.8 284.0  
Total assets 10,314.9   10,314.9   9,826.3
Operating Segments | Institutional          
Segment Reporting [Line Items]          
Non-interest revenues 355.9 233.4 1,093.2 671.8  
Interest income 519.4 392.6 1,516.5 1,055.0  
Total revenues 875.3 626.0 2,609.7 1,726.8  
Cost of sales of physical commodities 0.0 0.0 0.0 0.0  
Total operating revenues 875.3 626.0 2,609.7 1,726.8  
Transaction-based clearing expenses 101.0 67.5 298.6 197.6  
Introducing broker commissions 15.0 7.8 46.7 23.1  
Total interest expense 447.0 350.6 1,312.4 941.0  
Net operating revenues 312.3 200.1 952.0 565.1  
Variable compensation and benefits 119.8 63.7 341.3 182.4  
Net contribution 192.5 136.4 610.7 382.7  
Fixed compensation and benefits 31.7 21.6 94.8 62.0  
Trading systems and market information 10.8 8.1 32.6 23.7  
Professional fees (10.0) 6.2 8.2 12.8  
Non-trading technology and support 1.4 1.0 4.1 2.9  
Selling and marketing 1.0 0.6 3.5 2.4  
Travel and business development 3.3 1.8 9.4 6.1  
Depreciation and amortization 5.5 1.2 16.4 3.2  
Bad debts, net of recoveries 0.3 0.0 1.9 (0.1)  
Shared services 8.5 3.8 22.2 10.7  
Other fixed expenses 10.1 2.4 25.0 6.0  
Non-variable expenses 62.6 46.7 218.1 129.7  
Other gains (losses), net 0.0 (2.3) (2.5) (1.0)  
Income before tax 129.9 87.4 390.1 252.0  
Total assets 39,569.3   39,569.3   32,465.5
Operating Segments | Self-Directed/Retail          
Segment Reporting [Line Items]          
Non-interest revenues 89.3 102.3 274.9 300.2  
Interest income 7.0 8.4 22.3 24.3  
Total revenues 96.3 110.7 297.2 324.5  
Cost of sales of physical commodities 0.0 0.0 0.0 0.0  
Total operating revenues 96.3 110.7 297.2 324.5  
Transaction-based clearing expenses 3.3 3.6 11.4 10.2  
Introducing broker commissions 26.7 27.9 81.5 76.1  
Total interest expense 1.9 1.8 6.2 5.5  
Net operating revenues 64.4 77.4 198.1 232.7  
Variable compensation and benefits 4.8 3.7 14.2 11.1  
Net contribution 59.6 73.7 183.9 221.6  
Fixed compensation and benefits 8.6 8.0 24.5 26.1  
Trading systems and market information 3.5 3.5 9.6 10.3  
Professional fees 0.7 3.3 4.1 8.7  
Non-trading technology and support 1.5 2.0 5.2 6.7  
Selling and marketing 9.7 8.9 26.6 26.5  
Travel and business development 0.4 0.4 1.4 1.5  
Depreciation and amortization 3.0 3.2 9.8 12.8  
Bad debts, net of recoveries 0.0 0.4 0.6 1.5  
Shared services 4.0 1.6 10.9 7.0  
Other fixed expenses 3.3 3.7 17.8 9.7  
Non-variable expenses 34.7 35.0 110.5 110.8  
Other gains (losses), net 0.0 0.0 0.0 4.4  
Income before tax 24.9 38.7 73.4 115.2  
Total assets 1,500.7   1,500.7   1,256.2
Operating Segments | Payments          
Segment Reporting [Line Items]          
Non-interest revenues 59.9 53.0 172.3 160.3  
Interest income 0.4 0.3 1.0 1.4  
Total revenues 60.3 53.3 173.3 161.7  
Cost of sales of physical commodities 0.0 0.0 0.0 0.0  
Total operating revenues 60.3 53.3 173.3 161.7  
Transaction-based clearing expenses 2.5 1.9 6.7 5.4  
Introducing broker commissions 1.3 1.2 3.6 3.1  
Total interest expense 0.1 0.0 0.1 0.0  
Net operating revenues 56.4 50.2 162.9 153.2  
Variable compensation and benefits 9.4 8.9 26.8 26.8  
Net contribution 47.0 41.3 136.1 126.4  
Fixed compensation and benefits 4.6 7.1 14.8 21.1  
Trading systems and market information 0.2 0.2 0.6 0.9  
Professional fees 0.6 0.7 2.0 2.6  
Non-trading technology and support 0.3 0.4 1.0 1.4  
Selling and marketing 0.2 0.1 0.4 0.4  
Travel and business development 0.2 0.3 0.7 0.9  
Depreciation and amortization 1.5 1.2 4.1 3.4  
Bad debts, net of recoveries 0.0 0.0 0.0 0.0  
Shared services 3.8 2.1 9.2 6.3  
Other fixed expenses 1.0 1.1 2.4 2.7  
Non-variable expenses 12.4 13.2 35.2 39.7  
Other gains (losses), net (0.2) 0.0 (0.8) 0.0  
Income before tax 34.4 28.1 100.1 86.7  
Total assets 756.7   756.7   722.5
Corporate          
Segment Reporting [Line Items]          
Non-interest revenues (8.2) 7.3 4.8 13.2  
Interest income 11.0 8.4 29.9 30.3  
Total revenues 2.8 15.7 34.7 43.5  
Cost of sales of physical commodities 0.0 0.0 0.0 0.0  
Total operating revenues 2.8 15.7 34.7 43.5  
Transaction-based clearing expenses 1.8 1.2 6.7 4.2  
Introducing broker commissions 0.0 0.0 0.2 0.0  
Total interest expense 40.8 25.4 120.5 79.9  
Net operating revenues (39.8) (10.9) (92.7) (40.6)  
Variable compensation and benefits 29.4 23.1 69.3 62.0  
Net contribution (69.2) (34.0) (162.0) (102.6)  
Fixed compensation and benefits 80.5 66.8 243.0 197.0  
Trading systems and market information 5.9 5.1 18.2 12.8  
Professional fees 11.6 11.3 35.8 28.9  
Non-trading technology and support 25.7 17.3 72.5 49.5  
Selling and marketing 3.8 1.9 9.7 5.1  
Travel and business development 4.0 3.0 19.1 8.2  
Depreciation and amortization 11.2 7.3 31.2 20.9  
Bad debts, net of recoveries 0.0 0.0 0.0 0.0  
Shared services (28.8) (17.5) (75.9) (47.8)  
Other fixed expenses 26.2 22.1 79.5 61.1  
Non-variable expenses 140.1 117.3 433.1 335.7  
Other gains (losses), net (1.5) 0.0 (1.5) 0.0  
Income before tax (210.8) (151.3) (596.6) (438.3)  
Total assets 1,904.4   1,904.4   997.5
Eliminations          
Segment Reporting [Line Items]          
Non-interest revenues (2.5) (0.8) (4.2) (2.4)  
Interest income (16.4) (9.9) (54.9) (43.4)  
Total revenues (18.9) (10.7) (59.1) (45.8)  
Cost of sales of physical commodities 0.0 0.0 0.0 0.0  
Total operating revenues (18.9) (10.7) (59.1) (45.8)  
Transaction-based clearing expenses (0.8) (0.8) (2.5) (2.4)  
Introducing broker commissions (1.7) 0.0 (1.7) 0.0  
Total interest expense (16.4) (9.9) (54.9) (43.4)  
Net operating revenues 0.0 0.0 0.0 0.0  
Variable compensation and benefits 0.0 0.0 0.0 0.0  
Net contribution 0.0 0.0 0.0 0.0  
Fixed compensation and benefits 0.0 0.0 0.0 0.0  
Trading systems and market information 0.0 0.0 0.0 0.0  
Professional fees 0.0 0.0 0.0 0.0  
Non-trading technology and support 0.0 0.0 0.0 0.0  
Selling and marketing 0.0 0.0 0.0 0.0  
Travel and business development 0.0 0.0 0.0 0.0  
Depreciation and amortization 0.0 0.0 0.0 0.0  
Bad debts, net of recoveries 0.0 0.0 0.0 0.0  
Shared services 0.0 0.0 0.0 0.0  
Other fixed expenses 0.0 0.0 0.0 0.0  
Non-variable expenses 0.0 0.0 0.0 0.0  
Other gains (losses), net 0.0 0.0 0.0 0.0  
Income before tax 0.0 $ 0.0 0.0 $ 0.0  
Total assets $ 0.0   $ 0.0   $ 0.0