Legal Matters - Schedule of Accrued Litigation for Both Covered and Non-Covered Litigation (Detail) - USD ($) $ in Millions |
6 Months Ended | |
|---|---|---|
Mar. 31, 2025 |
Mar. 31, 2024 |
|
| Loss Contingency Accrual [Roll Forward] | ||
| Balance at beginning of period | $ 1,727 | $ 1,751 |
| Balance at end of period | 2,076 | 1,853 |
| Uncovered Litigation | ||
| Loss Contingency Accrual [Roll Forward] | ||
| Provision for legal matters | 25 | 310 |
| Covered Litigation | ||
| Loss Contingency Accrual [Roll Forward] | ||
| Provision for legal matters | 1,034 | 175 |
| Payments for legal matters | (710) | (383) |
| U.S. Covered Litigation | ||
| Loss Contingency Accrual [Roll Forward] | ||
| Balance at beginning of period | 1,537 | 1,621 |
| Provision for legal matters | 1,019 | 129 |
| Payments for legal matters | (580) | (204) |
| Balance at end of period | 1,976 | 1,546 |
| VE Territory Covered Litigation | ||
| Loss Contingency Accrual [Roll Forward] | ||
| Balance at beginning of period | 72 | 110 |
| Provision for legal matters | 15 | 46 |
| Payments for legal matters | (24) | (144) |
| Balance at end of period | $ 63 | $ 12 |