Fair Value Measurements and Investments - Schedule of Non-Marketable Equity Securities (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
Sep. 30, 2024 |
|
| Fair Value Disclosures [Abstract] | |||||
| Initial cost basis | $ 709 | $ 709 | $ 711 | ||
| Adjustments: | |||||
| Upward adjustments | 854 | 854 | 910 | ||
| Downward adjustments, including impairment | (495) | (495) | (465) | ||
| Carrying amount | 1,068 | 1,068 | $ 1,156 | ||
| Upward adjustments | 4 | $ 0 | 11 | $ 9 | |
| Downward adjustments, including impairment | $ (2) | $ (13) | $ (51) | $ (28) | |