Stockholders' Equity - Schedule of Effect of VE Territory Covered Losses Recovery on the Company Repurchasing its Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Sep. 30, 2025 |
Sep. 30, 2024 |
Sep. 30, 2023 |
|
| Conversion of Stock [Line Items] | |||
| Recovery through conversion rate adjustments | $ 0 | $ (6) | $ 1 |
| Series B preferred stock | |||
| Conversion of Stock [Line Items] | |||
| Reduction in equivalent number of class A common stock (in shares) | 1 | 5 | 0 |
| Effective price per share (in dollars per share) | $ 352.58 | $ 272.89 | $ 219.12 |
| Recovery through conversion rate adjustments | $ 5 | $ 161 | $ 19 |
| Anniversary Releases | $ 287 | $ 1,149 | $ 0 |
| Series C Preferred Stock | |||
| Conversion of Stock [Line Items] | |||
| Reduction in equivalent number of class A common stock (in shares) | 3 | 6 | 0 |
| Effective price per share (in dollars per share) | $ 353.32 | $ 273.24 | $ 215.28 |
| Recovery through conversion rate adjustments | $ 3 | $ 20 | $ 11 |
| Anniversary Releases | $ 1,137 | $ 1,569 | $ 0 |