Disclosures About Derivative Instruments and Hedging Activities (Details Textual) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended					12 Months Ended		12 Months Ended
	Aug. 31, 2011 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2012 Interest Rate Swaps [Member] EUR (€)	Sep. 30, 2011 Interest Rate Swaps [Member] EUR (€)	Sep. 30, 2012 Foreign Currency [Member] USD ($)	Sep. 30, 2011 Foreign Currency [Member] USD ($)	Sep. 30, 2012 Interest Rate Protection Agreements [Member] USD ($)	Sep. 30, 2011 Interest Rate Protection Agreements [Member] USD ($)	Sep. 30, 2012 Net Investment Hedges [Member] EUR (€)	Sep. 30, 2011 Net Investment Hedges [Member] EUR (€)	Sep. 30, 2012 Electric transmission congestion - Electric Utility [Member] kWh	Sep. 30, 2011 Electric transmission congestion - Electric Utility [Member] kWh	Sep. 30, 2012 Electric transmission congestion (excluding Electric Utility) [Member] kWh	Sep. 30, 2011 Electric transmission congestion (excluding Electric Utility) [Member] kWh	Sep. 30, 2012 LPG [Member] gal	Sep. 30, 2011 LPG [Member] gal	Sep. 30, 2012 Natural Gas [Member] DTH	Sep. 30, 2011 Natural Gas [Member] DTH	Sep. 30, 2012 Electricity (millions of kilowatt-hours) [Member] Call Option [Member] kWh	Sep. 30, 2011 Electricity (millions of kilowatt-hours) [Member] Call Option [Member] kWh	Sep. 30, 2012 Electricity (millions of kilowatt-hours) [Member] Put Option [Member] kWh	Sep. 30, 2011 Electricity (millions of kilowatt-hours) [Member] Put Option [Member] kWh	Sep. 30, 2012 Gas Utility [Member] DTH	Sep. 30, 2011 Gas Utility [Member] DTH	Sep. 30, 2012 Electric Utility - Forward Contract [Member] USD ($) kWh	Sep. 30, 2011 Electric Utility - Forward Contract [Member] USD ($) kWh	Sep. 30, 2012 Midstream And Marketing Natural Gas [Member] DTH	Sep. 30, 2012 Midstream And Marketing Propane Storage [Member] gal
Derivative [Line Items]
Notional amount (in units)													189,700,000	208,600,000	988,800,000	1,418,600,000	243,900,000	138,000,000	23,600,000	26,100,000	1,415,700,000	1,219,800,000	135,300,000	204,900,000	19,200,000	15,100,000	570,400,000	788,600,000	4,300,000	3,100,000
Maximum length of time hedged in price risk cash flow hedges							30 months						8 months				26 months		39 months		36 months		16 months		12 months		20 months
Fair values of electric utility's forward purchase power agreements			$ 132.9	$ 91.9																							$ 9.2	$ 8.7
Maximum period of hedging exposure to variability in cash flows associated with price risk, weighted average							11 months										5 months		11 months		10 months		8 months
Net losses associated with commodity price risk hedges expected to be reclassified into earnings during the next twelve months			(53.0)
Underlying variable rate debt					441.9	424.2	174.5	133.9	173.0	173.0	0	14.5
Recorded loss amount included in Other Income, Net									(0.7)
Amount of net losses associated with interest rate hedges to be reclassified with interest rate hedges during the next 12 months			(0.8)
Minimum approximate range of estimated dollar-denominated purchases of LPG							15.00%
Maximum approximate range of estimated dollar-denominated purchases of LPG							30.00%
Amount of net losses associated with currency rate risk to be reclassified into earnings during the next 12 months			1.8
Restricted Cash in brokerage accounts			3.0	17.2
Write off of settled but unamortized interest rate protection agreements included in extinguishment of debt	2.6
Long term debt not issued				150
Loss as a result of the discontinuance of cash flow hedge accounting		$ 12.2