Disclosures About Derivative Instruments and Hedging Activities (Details Textual) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended				9 Months Ended																						3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Jun. 30, 2012 USD ($) States	Sep. 30, 2011 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2012 Foreign Currency [Member] USD ($)	Jun. 30, 2011 Foreign Currency [Member] USD ($)	Jun. 30, 2012 Interest Rate Swaps [Member] EUR (€)	Jun. 30, 2011 Interest Rate Swaps [Member] EUR (€)	Jun. 30, 2012 Interest Rate Protection Agreements [Member] USD ($)	Jun. 30, 2011 Interest Rate Protection Agreements [Member] USD ($)	Jun. 30, 2012 Net Investment Hedges [Member] USD ($)	Jun. 30, 2011 Net Investment Hedges [Member] USD ($)	Jun. 30, 2012 LPG (millions of gallons) [Member] gal	Jun. 30, 2011 LPG (millions of gallons) [Member] gal	Jun. 30, 2012 Natural Gas (millions of dekatherms) [Member] DTH	Jun. 30, 2011 Natural Gas (millions of dekatherms) [Member] DTH	Jun. 30, 2012 Electricity (millions of kilowatt-hours) [Member] Calls [Member] kWh	Jun. 30, 2011 Electricity (millions of kilowatt-hours) [Member] Calls [Member] kWh	Jun. 30, 2012 Electricity (millions of kilowatt-hours) [Member] Puts [Member] kWh	Jun. 30, 2011 Electricity (millions of kilowatt-hours) [Member] Puts [Member] kWh	Jun. 30, 2012 Electric transmission congestion - Electric Utility [Member] kWh	Jun. 30, 2011 Electric transmission congestion - Electric Utility [Member] kWh	Jun. 30, 2012 Gas Utility [Member] DTH	Jun. 30, 2011 Gas Utility [Member] DTH	Jun. 30, 2012 Midstream & Marketing [Member] Electric transmission congestion (excluding Electric Utility) [Member] kWh	Jun. 30, 2011 Midstream & Marketing [Member] Electric transmission congestion (excluding Electric Utility) [Member] kWh	Jun. 30, 2012 Electric Utility - Forward Contract [Member] USD ($) kWh	Jun. 30, 2011 Electric Utility - Forward Contract [Member] USD ($) kWh	Jun. 30, 2012 Midstream and Marketing Natural Gas [Member] DTH	Jun. 30, 2012 Midstream and Marketing Propane Storage [Member] gal	Jun. 30, 2012 Derivatives Not Designated as Hedging Instruments [Member] USD ($)	Jun. 30, 2011 Derivatives Not Designated as Hedging Instruments [Member] USD ($)	Jun. 30, 2012 Derivatives Not Designated as Hedging Instruments [Member] USD ($)	Jun. 30, 2011 Derivatives Not Designated as Hedging Instruments [Member] USD ($)	Jun. 30, 2012 Derivatives Not Designated as Hedging Instruments [Member] Commodity Contracts [Member] USD ($) gal	Jun. 30, 2012 Cost of Sales [Member] Derivatives Not Designated as Hedging Instruments [Member] Commodity Contracts [Member] USD ($)	Jun. 30, 2011 Cost of Sales [Member] Derivatives Not Designated as Hedging Instruments [Member] Commodity Contracts [Member] USD ($)	Jun. 30, 2012 Cost of Sales [Member] Derivatives Not Designated as Hedging Instruments [Member] Commodity Contracts [Member] USD ($)	Jun. 30, 2011 Cost of Sales [Member] Derivatives Not Designated as Hedging Instruments [Member] Commodity Contracts [Member] USD ($)
Disclosures About Derivative Instruments Hedging Activities (Textual) [Abstract]
Notional amount (in units)												231,900,000	145,000,000	21,200,000	21,200,000	1,688,400,000	1,318,000,000	131,800,000	117,200,000	261,000,000	287,300,000	13,200,000	18,600,000	1,285,500,000	1,955,200,000	654,700,000	874,400,000	4,100,000	2,200,000					29,000,000
Maximum length of time hedged in price risk cash flow hedges (in months)				29 months								29 months		41 months		33 months		18 months				16 months		11 months		23 months
Underlying variable rate debt				$ 75.0	$ 141.4	€ 441.9	€ 398.8	$ 173.0	$ 173.0	$ 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	187.0		33.5																							13.1	10.1
Maximum period of hedging exposure to variability in cash flows associated with price risk, weighted average (in months)				13 months								7 months		11 months		9 months		10 months
Recorded loss amount included in Other Income, Net								0.7
Minimum approximate range of estimated dollar-denominated purchases of LPG (as a percent)				15.00%
Maximum approximate range of estimated dollar-denominated purchases of LPG (as a percent)				30.00%
Derivative Instruments, Gain (Loss) Recognized in Income, Net																														(16.0)	0.2	(12.0)	(0.1)	0	(15.9)	0.2	(12.6)	(0.4)
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	99.1
Amount of net losses associated with interest rate hedges to be reclassified with interest rate hedges during the next 12 months	0.9
Amount of net losses associated with currency rate risk to be reclassified into earnings during the next 12 months	3.2
Restricted Cash in brokerage accounts	$ 7.6	$ 17.2	$ 10.2
Transmission organization controls movements of wholesale electricity in number of states (in states)	14