Financial Instruments (Carrying Amount and Cumulative Hedging Adjustment) (Details) - Long-term debt - USD ($) $ in Millions |
Mar. 31, 2024 |
Sep. 30, 2023 |
|---|---|---|
| Derivative Instruments and Hedging Activities Disclosures [Line Items] | ||
| Carrying amounts of hedged item | $ 2,030.2 | $ 2,011.4 |
| Cumulative hedging adjustment, included in carrying amount | $ (62.6) | $ (80.5) |