Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Property, Plant and Equipment [Line Items]
Utilities	$ 2,427.8	$ 2,295.7
Non-utility	4,612.7	4,223.9
Total property, plant and equipment	7,040.5	6,519.6
Distribution [Member]
Property, Plant and Equipment [Line Items]
Utilities	2,162.6	2,047.8
Transmission [Member]
Property, Plant and Equipment [Line Items]
Utilities	86.6	85.4
General and other, including work in process [Member]
Property, Plant and Equipment [Line Items]
Utilities	178.6	162.5
Land [Member]
Property, Plant and Equipment [Line Items]
Non-utility	178.4	175.0
Building and improvements [Member]
Property, Plant and Equipment [Line Items]
Non-utility	308.1	282.0
Transportation equipment [Member]
Property, Plant and Equipment [Line Items]
Non-utility	273.8	246.5
Equipment, primarily cylinders and tanks [Member]
Property, Plant and Equipment [Line Items]
Non-utility	3,184.4	3,043.4
Electric generation [Member]
Property, Plant and Equipment [Line Items]
Non-utility	264.8	254.3
Other, including work in process [Member]
Property, Plant and Equipment [Line Items]
Non-utility	$ 403.2	$ 222.7