Investments - Narrative (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2026 |
Jun. 30, 2025 |
Sep. 30, 2025 |
|
| Investments, Debt and Equity Securities [Abstract] | ||||
| Cumulative upward adjustments from observed price | $ 23 | $ 23 | $ 23 | |
| Cumulative downward adjustments from impairments | 17 | 17 | $ 10 | |
| Unrealized losses on investments | $ 7 | $ 7 | $ 3 | |