Fair Value Measurements - Debt Securities, Trading, and Equity Securities, FV-NI (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
|
| Deferred compensation plan assets | ||||
| Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] | ||||
| Equity securities, FV-NI, unrealized gain (loss) | $ 4 | $ 0 | $ 2 | $ 7 |
| Investments in exchange traded funds | ||||
| Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] | ||||
| Equity securities, FV-NI, unrealized gain (loss) | $ 20 | $ 4 | $ 12 | $ 43 |