Income Taxes - Reconciliation of Beginning and Ending Unrecognized Tax Benefits by Fiscal Year (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Sep. 30, 2023 |
Sep. 30, 2022 |
Sep. 30, 2021 |
|
| Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] | |||
| Balance as of beginning of period | $ 2,683 | $ 2,488 | $ 2,579 |
| Increase in unrecognized tax benefits related to prior years | 515 | 10 | 34 |
| Decrease in unrecognized tax benefits related to prior years | (190) | (143) | (386) |
| Increase in unrecognized tax benefits related to current year | 510 | 350 | 326 |
| Decrease related to settlements with taxing authorities | (17) | (19) | (63) |
| Reduction related to lapsing statute of limitations | (4) | (3) | (2) |
| Balance as of end of period | $ 3,497 | $ 2,683 | $ 2,488 |