Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Property, Plant and Equipment
Utilities	$ 2,568.5	$ 2,427.8
Non-utility	4,608.2	4,612.7
Total property, plant and equipment	7,176.7	7,040.5
Distribution
Property, Plant and Equipment
Utilities	2,294.6	2,162.6
Transmission
Property, Plant and Equipment
Utilities	88.2	86.6
General and Other, Including Work-in-Process
Property, Plant and Equipment
Utilities	185.7	178.6
Land
Property, Plant and Equipment
Non-utility	170.2	178.4
Building and Improvements
Property, Plant and Equipment
Non-utility	317.4	308.1
Transportation Equipment
Property, Plant and Equipment
Non-utility	288.4	273.8
Equipment, Primarily Cylinders and Tanks
Property, Plant and Equipment
Non-utility	3,042.7	3,161.9
Electric Generation
Property, Plant and Equipment
Non-utility	273.4	264.8
Pipeline and Related Assets
Property, Plant and Equipment
Non-utility	162.3	22.5
Other, Including Work-in-Process
Property, Plant and Equipment
Non-utility	$ 353.8	$ 403.2