Property, Plant and Equipment (Details) (USD $) In Millions	Sep. 30, 2011	Sep. 30, 2010
Property, Plant and Equipment [Line Items]
Utilities	$ 2,201.0	$ 2,129.3
Non-utility	3,083.5	2,840.4
Total property, plant and equipment	5,284.5	4,969.7
Distribution [Member]
Property, Plant and Equipment [Line Items]
Utilities	1,951.9	1,866.0
Transmission [Member]
Property, Plant and Equipment [Line Items]
Utilities	83.4	78.2
General and Other Including Work in Process [Member]
Property, Plant and Equipment [Line Items]
Utilities	165.7	185.1
Land [Member]
Property, Plant and Equipment [Line Items]
Non-utility	98.5	94.1
Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Non-utility	214.8	206.4
Transportation Equipment [Member]
Property, Plant and Equipment [Line Items]
Non-utility	112.6	111.3
Equipment Primarily Cylinders and Tanks [Member]
Property, Plant and Equipment [Line Items]
Non-utility	2,127.6	2,020.3
Electric Generation [Member]
Property, Plant and Equipment [Line Items]
Non-utility	230.0	97.9
Other, including work in process [Member]
Property, Plant and Equipment [Line Items]
Non-utility	$ 300.0	$ 310.4