Supplemental Information (Shareholder Activism Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Shareholder Activism Costs [Line Items]
Legal, executive separation, and other professional service fees in connection with response to proxy contest	$ 31.4	$ 0.0	$ 61.3	$ 0.0
Legal, executive separation, and other professional service fees in connection with response to proxy contest, after tax	31.0		52.9
Business and asset actions	2,927.9	$ 57.0	$ 2,927.9	$ 57.0
Executive Separation Costs
Shareholder Activism Costs [Line Items]
Share-based payment arrangement, accelerated cost	22.4
Business and asset actions	$ 7.3