Plant and Equipment, Net (Major Classes of Plant and Equipment) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 28,160.1	$ 27,488.8
Less: Accumulated depreciation	13,999.6	14,234.2
Plant and equipment, net	14,160.5	13,254.6	$ 11,964.7
Land
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	266.7	312.1
Buildings
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 1,431.3	1,083.1
Useful life (in years)	30 years
Production facilities
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 18,000.5	18,236.9
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	$ 4,784.9	5,111.6
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	$ 3,676.7	$ 2,745.1