Stockholders' Equity - Schedule of Effect of U.S. Retrospective Responsibility Plan on the Company Class Common B As-Converted Shares (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Sep. 30, 2025 |
Sep. 30, 2024 |
Sep. 30, 2023 |
|
| Equity [Abstract] | |||
| Reduction in equivalent number of class A common stock (in shares) | 3 | 5 | 5 |
| Effective price per share (in dollars per share) | $ 343.41 | $ 274.62 | $ 221.33 |
| Deposits into the U.S. litigation escrow account | $ 875 | $ 1,500 | $ 1,000 |