Significant Accounting Policies (Details Textual) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Accounting Policies [Abstract]
Ownership interests in certain subsidiaries under equity method investment	100% or Less
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	20% or Less
Voting rights in investment businesses not traded publicly accounted for under the cost method, maximum	20.00%
Investments in other assets	$ 80.0	$ 72.4
Interest (income) expense on tax deficiencies and penalties	(0.1)	0.2	(0.2)
Antidilutive outstanding stock option award	81,000	3,700,000
Reclassification of benefit plans actuarial losses and prior service costs net of tax to regulatory assets			83.3
Maturities Period of highly liquid investments	three months or less
Estimated maximum period of capitalized and amortized costs to install partnership and antargaz-owned tanks	10 years
Maximum period of benefit for computer software amortization expense	15 years
Net deferred debt issuance costs	46.6	30.7
Foreign subsidiary customer deposits	$ 205.1	$ 204.4
Average to Include Prudently Incurred Remediation Costs	5 years
Building and Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life (in years)	15 years
Building and Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life (in years)	40 years
Storage and customer tanks and cylinders [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life (in years)	7 years
Storage and customer tanks and cylinders [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life (in years)	40 years
Electric Utility [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense as percentage of related average depreciable base	2.40%	2.60%	2.60%
Electric Generation, Transmission and Distribution Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life (in years)	25 years
Electric Generation, Transmission and Distribution Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life (in years)	35 years
Vehicles, equipment and office furniture and fixtures [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life (in years)	2 years
Vehicles, equipment and office furniture and fixtures [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life (in years)	12 years
Gas Utility [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense as percentage of related average depreciable base	2.20%	2.30%	2.50%