Business and Asset Actions (Project Exit Costs Narrative) (Details) $ in Millions	12 Months Ended
	Sep. 30, 2025 USD ($) plant project	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Project exit costs	$ 3,623.3	$ 0.0	$ 217.6
Assets held for sale	427.7	0.0
Liabilities held for sale	50.5	0.0
Plant and equipment, net	25,337.8	$ 23,370.9	17,472.1
Project Exit Costs
Restructuring Cost and Reserve [Line Items]
Project exit costs	$ 3,623.3		$ 217.6
Number of plants to be disposed of | plant	2
Impairment of property and equipment	$ 2,500.0
Project Exit Costs | Fair Value, Nonrecurring
Restructuring Cost and Reserve [Line Items]
Plant and equipment held for sale	418.3
Plant and equipment, net	22.5
Project Exit Costs | U.S.-based projects [Member]
Restructuring Cost and Reserve [Line Items]
Project exit costs	$ 2,400.0
Number of projects eliminated | project	3
Project Exit Costs | Other global projects [Member]
Restructuring Cost and Reserve [Line Items]
Project exit costs	$ 755.0
Project Exit Costs | Coal gasification plants
Restructuring Cost and Reserve [Line Items]
Project exit costs	$ 425.0
Number of plants to be disposed of | plant	2
Impairment of property and equipment	$ 350.6
Project Exit Costs | Coal gasification plants | Fair Value, Nonrecurring
Restructuring Cost and Reserve [Line Items]
Plant and equipment held for sale	$ 418.3