Share-Based Compensation (Compensation Cost Recognized in Income Statement) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Mar. 31, 2024 |
Mar. 31, 2023 |
Mar. 31, 2024 |
Mar. 31, 2023 |
|
| Share-based Payment Arrangement, Additional Disclosure [Abstract] | ||||
| Before-tax share-based compensation cost | $ 14.8 | $ 15.5 | $ 28.4 | $ 32.4 |
| Income tax benefit | (3.6) | (3.9) | (6.9) | (7.9) |
| After-tax share-based compensation cost | $ 11.2 | $ 11.6 | $ 21.5 | $ 24.5 |