Summary of Significant Accounting Policies (Details) (USD $)	0 Months Ended	12 Months Ended
	Jul. 29, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Accounting Policies [Abstract]
Ownership interests in certain subsidiaries under equity method investment, maximum		100.00%
Voting rights in investment businesses not traded publicly accounted for under the cost method, maximum		20.00%
Maturities Period of highly liquid investments		three months or less
Accumulated impairment losses		$ 0
Provision for goodwill or other intangible asset impairments		0	0	0
Provisions for impairments		0	0	0
Other-than-temporary impairment of an investment in a private equity partnership pre-tax loss		0	6,300,000	0
Net deferred debt issuance costs		36,700,000	39,400,000
Foreign subsidiary customer deposits		200,000,000	214,600,000
Average to include prudently incurred remediation costs		5 years
Property, Plant and Equipment
Stockholders' Equity Note, Stock Split, Conversion Ratio	1.5
Estimated maximum period of capitalized and amortized costs to install partnership and antargaz-owned tanks		10 years
Estimated useful life of definite-lived intangible assets		15 years
Gas Utility
Property, Plant and Equipment
Depreciation expense as percentage of related average depreciable base		2.30%	2.30%	2.20%
Electric Utility
Property, Plant and Equipment
Depreciation expense as percentage of related average depreciable base		2.50%	2.40%	2.40%
Non-utility Plant and Equipment | Minimum
Property, Plant and Equipment
Useful life (in years)		10 years
Non-utility Plant and Equipment | Maximum
Property, Plant and Equipment
Useful life (in years)		40 years
Storage and Customer Tanks and Cylinders | Minimum
Property, Plant and Equipment
Useful life (in years)		6 years
Storage and Customer Tanks and Cylinders | Maximum
Property, Plant and Equipment
Useful life (in years)		40 years
Electricity Generation Facilities | Minimum
Property, Plant and Equipment
Useful life (in years)		25 years
Electricity Generation Facilities | Maximum
Property, Plant and Equipment
Useful life (in years)		40 years
Pipeline and Related Assets | Minimum
Property, Plant and Equipment
Useful life (in years)		25 years
Pipeline and Related Assets | Maximum
Property, Plant and Equipment
Useful life (in years)		40 years
Vehicles, Equipment and Office Furniture and Fixtures | Minimum
Property, Plant and Equipment
Useful life (in years)		3 years
Vehicles, Equipment and Office Furniture and Fixtures | Maximum
Property, Plant and Equipment
Useful life (in years)		12 years
Software and Software Development Costs [Member] | Maximum
Property, Plant and Equipment
Useful life (in years)		10 years
Other Assets
Property, Plant and Equipment
Cost method investments		77,800,000	82,000,000
Other Assets | Private Equity Partnership That Invests in Renewable Energy Companies
Property, Plant and Equipment
Cost method investments		$ 17,400,000	$ 16,400,000
Interest in a private equity partnership		3.50%