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