COLLATERALIZED AGREEMENTS AND FINANCINGS, Collateral (Details) - USD ($) $ in Millions |
Mar. 31, 2026 |
Sep. 30, 2025 |
|---|---|---|
| Collateral Received that Can be Resold or Repledged [Abstract] | ||
| Collateral we received that was available to be delivered or repledged | $ 4,347 | $ 4,003 |
| Collateral that we delivered or repledged | $ 2,025 | $ 2,080 |