Stockholders' Equity - 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, 2024 |
Sep. 30, 2023 |
Sep. 30, 2022 |
|
| Conversion of Stock [Line Items] | |||
| Recovery through conversion rate adjustment | $ (6) | $ 1 | $ 0 |
| Series B preferred stock | |||
| Conversion of Stock [Line Items] | |||
| Reduction in equivalent number of class A common stock (in shares) | 5 | 0 | 8 |
| Effective price per share (in dollars per share) | $ 272.89 | $ 219.12 | $ 197.93 |
| Recovery through conversion rate adjustment | $ 161 | $ 19 | $ 135 |
| Anniversary Releases | $ 1,149 | $ 0 | $ 1,510 |
| Series C Preferred Stock | |||
| Conversion of Stock [Line Items] | |||
| Reduction in equivalent number of class A common stock (in shares) | 6 | 0 | 10 |
| Effective price per share (in dollars per share) | $ 273.24 | $ 215.28 | $ 197.50 |
| Recovery through conversion rate adjustment | $ 20 | $ 11 | $ 6 |
| Anniversary Releases | $ 1,569 | $ 0 | $ 1,982 |