Income Taxes - Effective Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ (505.8)	$ 130.5	$ (365.1)	$ 265.9
Effective tax rate	22.50%	18.30%	25.10%	18.10%
Business and asset actions, including equity affiliate income	$ 2,934.7		$ 2,934.7