Derivative Instruments and Hedging Activities (Details) In Millions, unless otherwise specified	3 Months Ended									3 Months Ended			3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended						3 Months Ended			3 Months Ended
	Dec. 31, 2014 USD ($) gal	Dec. 31, 2013 USD ($) gal	Sep. 30, 2014 USD ($)	Dec. 31, 2014 Brokerage Accounts USD ($)	Dec. 31, 2013 Brokerage Accounts USD ($)	Dec. 31, 2014 Interest Rate Swaps EUR (€)	Dec. 31, 2013 Interest Rate Swaps EUR (€)	Dec. 31, 2014 Interest Rate Protection Agreements USD ($)	Dec. 31, 2013 Interest Rate Protection Agreements USD ($)	Dec. 31, 2014 Foreign Currency USD ($)	Dec. 31, 2013 Foreign Currency USD ($)	Dec. 31, 2014 Cross Currency Contracts USD ($)	Dec. 31, 2014 Gas Utility DTH	Dec. 31, 2013 Gas Utility DTH	Dec. 31, 2014 Electric Utility kWh	Dec. 31, 2013 Electric Utility kWh	Dec. 31, 2014 Midstream & Marketing Electricity (millions of kilowatt-hours) Forward Purchase Contracts kWh	Dec. 31, 2013 Midstream & Marketing Electricity (millions of kilowatt-hours) Forward Purchase Contracts kWh	Dec. 31, 2014 Midstream & Marketing Electricity (millions of kilowatt-hours) Forward Sales Contracts kWh	Dec. 31, 2013 Midstream & Marketing Electricity (millions of kilowatt-hours) Forward Sales Contracts kWh	Dec. 31, 2014 Midstream & Marketing Propane Storage (millions of dekatherms) Forward Sales Contracts gal	Dec. 31, 2013 Midstream & Marketing Propane Storage (millions of dekatherms) Forward Sales Contracts gal	Dec. 31, 2014 Midstream & Marketing Gas Utility Natural Gas Forward Purchase Contracts DTH	Dec. 31, 2013 Midstream & Marketing Gas Utility Natural Gas Forward Purchase Contracts DTH	Dec. 31, 2014 Midstream & Marketing Natural Gas	Dec. 31, 2014 Midstream & Marketing Natural Gas Storage Forward Sales Contracts DTH	Dec. 31, 2013 Midstream & Marketing Natural Gas Storage Forward Sales Contracts DTH	Dec. 31, 2014 Midstream & Marketing FTR and NYISO Contracts	Dec. 31, 2014 Midstream & Marketing FTR and NYISO Contracts Electric transmission congestion (excluding Electric Utility) kWh	Dec. 31, 2013 Midstream & Marketing FTR and NYISO Contracts Electric transmission congestion (excluding Electric Utility) kWh	Dec. 31, 2014 Net Investment Hedging EUR (€)	Dec. 31, 2013 Net Investment Hedging EUR (€)
Derivative
Volume of LPG commodity derivatives (in gallons)	429,600,000	215,200,000
Maximum length of time hedging exposure to LPG commodity price risk	33 months
Outstanding derivative commodity instruments volumes													11,200,000	9,700,000	486,200,000	324,400,000	350,000,000	664,700,000	184,100,000	371,000,000	2,600,000	2,200,000	70,000,000	27,400,000		600,000	1,100,000		331,800,000	1,085,900,000
Maximum length of time hedged in price risk cash flow hedges										36 months			9 months		17 months		24 months		9 months						41 months			5 months
Notional amount						€ 401.1	€ 439.8	$ 0	$ 0	$ 225.8	$ 149.1	$ 52.0																			€ 0	€ 0
Amount of net losses associated with interest rate hedges to be reclassified with interest rate hedges during the next 12 months	2.7
Amount of net gains associated with currency rate risk to be reclassified into earnings during the next 12 months	8.7
Restricted cash	$ 54.6	$ 4.5	$ 16.6	$ 54.6	$ 3.2