Disclosures About Derivative Instruments and Hedging Activities (Details Textual) In Millions, unless otherwise specified	6 Months Ended			6 Months Ended				6 Months Ended
	Mar. 31, 2012 USD ($) States	Sep. 30, 2011 USD ($)	Mar. 31, 2011 USD ($)	Mar. 31, 2012 Foreign Currency [Member] USD ($)	Mar. 31, 2011 Foreign Currency [Member] USD ($)	Mar. 31, 2012 Interest Rate Swaps [Member] EUR (€)	Mar. 31, 2011 Interest Rate Swaps [Member] EUR (€)	Mar. 31, 2012 Interest Rate Protection Agreements [Member] USD ($)	Mar. 31, 2011 Interest Rate Protection Agreements [Member] USD ($)	Mar. 31, 2012 Net Investment Hedges [Member] EUR (€)	Mar. 31, 2011 Net Investment Hedges [Member] EUR (€)	Mar. 31, 2012 LPG [Member] gal	Mar. 31, 2011 LPG [Member] gal	Mar. 31, 2012 Natural Gas [Member] DTH	Mar. 31, 2011 Natural Gas [Member] DTH	Mar. 31, 2012 Electricity (millions of kilowatt-hours) [Member] Calls [Member] kWh	Mar. 31, 2011 Electricity (millions of kilowatt-hours) [Member] Calls [Member] kWh	Mar. 31, 2012 Electricity (millions of kilowatt-hours) [Member] Puts [Member] kWh	Mar. 31, 2012 Electric transmission congestion - Electric Utility [Member] kWh	Mar. 31, 2011 Electric transmission congestion - Electric Utility [Member] kWh	Mar. 31, 2012 Gas Utility [Member] DTH	Mar. 31, 2011 Gas Utility [Member] DTH	Mar. 31, 2012 Midstream & Marketing [Member] Electric transmission congestion (excluding Electric Utility) [Member] kWh	Mar. 31, 2011 Midstream & Marketing [Member] Electric transmission congestion (excluding Electric Utility) [Member] kWh	Mar. 31, 2012 Electric Utility - Forward Contract [Member] USD ($) kWh	Mar. 31, 2011 Electric Utility - Forward Contract [Member] USD ($) kWh	Mar. 31, 2012 Midstream and Marketing Natural Gas [Member] DTH	Mar. 31, 2012 Midstream and Marketing Propane Storage [Member] gal
Disclosures About Derivative Instruments Hedging Activities (Textual) [Abstract]
Notional amount (in units)												146,800,000	47,300,000	22,800,000	21,900,000	1,793,900,000	1,516,200,000	153,600,000	52,200,000	138,200,000	11,600,000	21,500,000	355,800,000	257,700,000	707,400,000	835,500,000	4,600,000	1,200,000
Maximum length of time hedged in price risk cash flow hedges				23 months								21 months		36 months		34 months		21 months			19 months		2 months		26 months
Underlying variable rate debt				$ 63.9	$ 69.8	€ 442.6	€ 399.5	$ 173.0	$ 106.5	€ 14.5	€ 14.5
Maximum length of time hedged in price risk cash flow hedges										September 2012
Fair values of electric utility's forward purchase power agreements	136.5		24.6																						14.7	10.7
Maximum period of hedging exposure to variability in cash flows associated with price risk, weighted average				13 months								8 months		12 months		9 months		11 months
Recorded loss amount included in Other Income, Net								0.7
Minimum approximate range of estimated dollar-denominated purchases of LPG				15.00%
Maximum approximate range of estimated dollar-denominated purchases of LPG				30.00%
Disclosures About Derivative Instruments Hedging Activities (Additional Textual) [Abstract]
Net losses associated with commodity price risk hedges expected to be reclassified into earnings during the next twelve months	71.6
Amount of net losses associated with interest rate hedges to be reclassified with interest rate hedges during the next 12 months	1.0
Amount of net losses associated with currency rate risk to be reclassified into earnings during the next 12 months	1.0
Restricted Cash in brokerage accounts	$ 16.8	$ 17.2	$ 9.6
Transmission organization controls movements of wholesale electricity in number of states	14