Pension and Other Postretirement Benefits - Defined contribution plan expense (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Sep. 30, 2024 |
Sep. 30, 2023 |
Sep. 30, 2022 |
|
| Retirement Benefits [Abstract] | |||
| 401K Matching Contributions | $ 27.3 | $ 21.4 | $ 19.6 |