Settlement Guarantee Management (Details) - USD ($) $ in Billions |
6 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Sep. 30, 2025 |
|
| Settlement Guarantee Management [Abstract] | ||
| Maximum settlement exposure | $ 168.6 | |
| Average daily settlement exposure | 98.1 | |
| Total collateral | $ 9.5 | $ 8.8 |