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, 2022 |
Sep. 30, 2021 |
Sep. 30, 2020 |
|
| Conversion of Stock [Line Items] | |||
| Recovery through conversion rate adjustment | $ 0 | $ (2) | $ 5 |
| Series B | |||
| Conversion of Stock [Line Items] | |||
| Reduction in equivalent number of class A common stock (in shares) | 8 | 0 | 16 |
| Effective price per share (in dollars per share) | $ 197.93 | $ 220.84 | $ 194.31 |
| Recovery through conversion rate adjustment | $ 135 | $ 35 | $ 72 |
| Anniversary Releases | $ 1,510 | $ 0 | $ 3,084 |
| Series C | |||
| Conversion of Stock [Line Items] | |||
| Reduction in equivalent number of class A common stock (in shares) | 10 | 0 | 22 |
| Effective price per share (in dollars per share) | $ 197.50 | $ 220.71 | $ 194.33 |
| Recovery through conversion rate adjustment | $ 6 | $ 20 | $ 92 |
| Anniversary Releases | $ 1,982 | $ 0 | $ 4,216 |