Other Required Disclosures - Components of Properties (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Sep. 30, 2012
Property, Plant and Equipment [Line Items]
Oil and Gas Properties Unproved	$ 49.8	$ 0
Oil and natural gas properties (full accounting method)	583.1	0
Less: Accumulated depletion	18.0	0
Total oil and natural gas properties, net	614.9	0
Total properties, at cost	656.4	437.7
Less accumulated depreciation	271.9	216.1
Properties, net	384.5	221.6
Property, Plant and Equipment including Oil and Gas Property, Net	999.4	221.6
Land, buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Total properties, at cost	160.4	93.6
Gas Gathering and Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Total properties, at cost	21.6
Machinery, equipment and other [Member]
Property, Plant and Equipment [Line Items]
Total properties, at cost	431.9	325.7
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Total properties, at cost	$ 42.5	$ 18.4