Share-Based Compensation (Compensation Cost Recognized in Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Before-tax share-based compensation cost	$ 38.3	$ 14.8	$ 54.8	$ 28.4
Income tax benefit	(9.0)	(3.6)	(13.0)	(6.9)
After-tax share-based compensation cost	29.3	$ 11.2	$ 41.8	$ 21.5
Executive Separation Costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, accelerated cost	$ 22.4