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, 2023 |
Sep. 30, 2022 |
Sep. 30, 2021 |
|
| Conversion of Stock [Line Items] | |||
| Recovery through conversion rate adjustment | $ 1 | $ 0 | $ (2) |
| Series B preferred stock | |||
| Conversion of Stock [Line Items] | |||
| Reduction in equivalent number of class A common stock (in shares) | 0 | 8 | 0 |
| Effective price per share (in dollars per share) | $ 219.12 | $ 197.93 | $ 220.84 |
| Recovery through conversion rate adjustment | $ 19 | $ 135 | $ 35 |
| Sixth Anniversary Release | $ 0 | $ 1,510 | $ 0 |
| Series C | |||
| Conversion of Stock [Line Items] | |||
| Reduction in equivalent number of class A common stock (in shares) | 0 | 10 | 0 |
| Effective price per share (in dollars per share) | $ 215.28 | $ 197.50 | $ 220.71 |
| Recovery through conversion rate adjustment | $ 11 | $ 6 | $ 20 |
| Sixth Anniversary Release | $ 0 | $ 1,982 | $ 0 |