Share-Based Compensation (Compensation Cost Recognized in Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Share-Based Payment Arrangement [Abstract]
Before-tax share-based compensation cost(A)	$ 16.0	$ 38.3	$ 26.3	$ 54.8
Income tax benefit	(3.8)	(9.0)	(6.2)	(13.0)
After-tax share-based compensation cost	$ 12.2	29.3	$ 20.1	41.8
Executive Separation Costs
Share-Based Payment Arrangement [Abstract]
Share-based payment arrangement, accelerated cost		22.4		22.4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, accelerated cost		$ 22.4		$ 22.4