Fair Value Measurements - Debt Securities, Trading, and Equity Securities, FV-NI (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Dec. 31, 2023 |
Dec. 31, 2022 |
|
| 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 | $ 3 |
| 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) | $ 22 | $ 11 |