Stockholders' Equity - Share Repurchases in the Open Market (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Mar. 31, 2025 |
Mar. 31, 2024 |
Mar. 31, 2025 |
Mar. 31, 2024 |
Sep. 30, 2024 |
|
| Equity, Class of Treasury Stock [Line Items] | |||||
| Total cost | $ 4,473 | $ 2,784 | $ 8,413 | $ 6,393 | |
| Unsettled repurchases | $ 4,507 | $ 4,507 | $ 4,909 | ||
| Class A common stock | |||||
| Equity, Class of Treasury Stock [Line Items] | |||||
| Shares repurchased in the open market (in shares) | 13 | 10 | 26 | 25 | |
| Average repurchase cost per share (in dollars per share) | $ 340.26 | $ 280.41 | $ 320.47 | $ 255.09 | |
| Total cost | $ 4,473 | $ 2,784 | $ 8,413 | $ 6,393 | |
| Unsettled repurchases | $ 61 | $ 61 | |||