COMMITMENTS, CONTINGENCIES AND GUARANTEES, Summary of Off-Balance Sheet Risks (Details) - USD ($) $ in Millions |
Mar. 31, 2026 |
Sep. 30, 2025 |
|---|---|---|
| Commitments and Contingencies Disclosure [Abstract] | ||
| SBL and other consumer lines of credit | $ 63,401 | $ 56,048 |
| Commercial lines of credit | 5,415 | 5,441 |
| Unfunded lending commitments | 523 | 716 |
| Standby letters of credit | $ 233 | $ 217 |