Plant and Equipment, Net (Major Classes of Plant and Equipment) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 32,746.3	$ 28,160.1
Less: Accumulated depreciation	15,274.2	13,999.6
Plant and equipment, net	17,472.1	14,160.5	$ 13,254.6
Land
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	320.8	266.7
Buildings
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 1,543.7	1,431.3
Useful life (in years)	30 years
Production facilities
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 19,593.1	18,000.5
Production facilities | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	10 years
Production facilities | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	20 years
Distribution and other machinery and equipment
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 5,129.6	4,784.9
Distribution and other machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Distribution and other machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	25 years
Cylinders | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	10 years
Cylinders | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	25 years
Tanks
Property, Plant and Equipment [Line Items]
Useful life (in years)	20 years
Customer Stations
Property, Plant and Equipment [Line Items]
Useful life (in years)	7 years 6 months
Tractors and Trailers | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Tractors and Trailers | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	15 years
Construction in progress
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 6,159.1	$ 3,676.7