Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011
Property, Plant and Equipment [Line Items]
Utilities	$ 2,295.7	$ 2,201.0
Non-utility	4,223.4	3,083.5
Total property, plant and equipment	6,519.1	5,284.5
Distribution [Member]
Property, Plant and Equipment [Line Items]
Utilities	2,047.8	1,951.9
Transmission [Member]
Property, Plant and Equipment [Line Items]
Utilities	85.4	83.4
General and other, including work in process [Member]
Property, Plant and Equipment [Line Items]
Utilities	162.5	165.7
Land [Member]
Property, Plant and Equipment [Line Items]
Non-utility	175.0	98.5
Building and improvements [Member]
Property, Plant and Equipment [Line Items]
Non-utility	283.3	214.8
Transportation equipment [Member]
Property, Plant and Equipment [Line Items]
Non-utility	246.5	112.6
Equipment, primarily cylinders and tanks [Member]
Property, Plant and Equipment [Line Items]
Non-utility	3,041.1	2,127.6
Electric generation [Member]
Property, Plant and Equipment [Line Items]
Non-utility	254.3	230.0
Other, including work in process [Member]
Property, Plant and Equipment [Line Items]
Non-utility	$ 223.2	$ 300.0