Plant and Equipment, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 884.7	$ 920.0
Less: accumulated depreciation	588.2	618.9
Plant and equipment, net	296.5	301.1	$ 351.9
Land
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 21.9	22.8
Buildings
Property, Plant and Equipment [Line Items]
Useful Life in years	30 years
Plant and equipment, at cost	$ 147.1	150.6
Machinery and Equipment
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	689.5	737.3
Production facilities
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 433.6	464.6
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	15 years
Distribution and other
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 255.9	272.7
Distribution and other | Minimum
Property, Plant and Equipment [Line Items]
Useful Life in years	5 years
Distribution and other | 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
Other distribution equipment
Property, Plant and Equipment [Line Items]
Useful Life in years	20 years
Construction in progress
Property, Plant and Equipment [Line Items]
Plant and equipment, at cost	$ 26.2	$ 9.3