Revenue Recognition (Nature of Goods and Services) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Change in Accounting Estimate [Line Items]
Operating income (loss)	$ 2,494.6	$ 2,338.8	$ 2,281.4
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]
Operating income (loss)	$ (115.0)	$ (30.0)	$ (19.0)