Revenue Recognition (Nature of Goods and Services) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Change in Accounting Estimate [Line Items]
Unfavorable impact on operating income	$ 877.0	$ (4,466.1)	$ (2,494.6)
On-site gases, large volume | Minimum
Change in Accounting Estimate [Line Items]
Sales contract term	15 years
On-site gases, large volume | Maximum
Change in Accounting Estimate [Line Items]
Sales contract term	20 years
On-site gases, small quantity | Minimum
Change in Accounting Estimate [Line Items]
Sales contract term	10 years
On-site gases, small quantity | Maximum
Change in Accounting Estimate [Line Items]
Sales contract term	15 years
Merchant gases | Maximum
Change in Accounting Estimate [Line Items]
Sales contract term	5 years
Contracts accounted for under percentage of completion
Change in Accounting Estimate [Line Items]
Unfavorable impact on operating income	$ 85.0	$ 175.0	$ 115.0