Disclosures About Derivative Instruments and Hedging Activities - Narrative (Details) In Millions, unless otherwise specified	6 Months Ended											6 Months Ended
	Mar. 31, 2014 USD ($)	Sep. 30, 2013 USD ($)	Mar. 31, 2013 USD ($)	Mar. 31, 2014 LPG (millions of gallons) gal	Mar. 31, 2013 LPG (millions of gallons) gal	Mar. 31, 2014 Brokerage Accounts USD ($)	Mar. 31, 2013 Brokerage Accounts USD ($)	Mar. 31, 2014 Interest Rate Swaps EUR (€)	Mar. 31, 2013 Interest Rate Swaps EUR (€)	Mar. 31, 2014 Interest Rate Protection Agreements USD ($)	Mar. 31, 2013 Interest Rate Protection Agreements USD ($)	Mar. 31, 2014 Foreign Currency USD ($)	Mar. 31, 2013 Foreign Currency USD ($)	Mar. 31, 2014 Cross Currency Interest Rate Contract USD ($)	Mar. 31, 2014 Gas Utility DTH	Mar. 31, 2013 Gas Utility DTH	Mar. 31, 2014 Electric Utility USD ($) kWh	Mar. 31, 2013 Electric Utility USD ($) kWh	Mar. 31, 2014 Midstream & Marketing Electric transmission congestion - Electric Utility kWh	Mar. 31, 2013 Midstream & Marketing Electric transmission congestion - Electric Utility kWh	Mar. 31, 2014 Midstream & Marketing Electric transmission congestion (excluding Electric Utility) kWh	Mar. 31, 2013 Midstream & Marketing Electric transmission congestion (excluding Electric Utility) kWh	Mar. 31, 2014 Midstream & Marketing Electricity (millions of kilowatt-hours) Forward Purchase Contracts kWh	Mar. 31, 2013 Midstream & Marketing Electricity (millions of kilowatt-hours) Forward Purchase Contracts kWh	Mar. 31, 2014 Midstream & Marketing Electricity (millions of kilowatt-hours) Forward Sales Contracts kWh	Mar. 31, 2013 Midstream & Marketing Electricity (millions of kilowatt-hours) Forward Sales Contracts kWh	Mar. 31, 2014 Midstream & Marketing Propane Storage (millions of dekatherms) Forward Sales Contracts gal	Mar. 31, 2013 Midstream & Marketing Propane Storage (millions of dekatherms) Forward Sales Contracts gal	Mar. 31, 2014 Midstream & Marketing Gas Utility Natural Gas Forward Purchase Contracts DTH	Mar. 31, 2013 Midstream & Marketing Gas Utility Natural Gas Forward Purchase Contracts DTH	Mar. 31, 2014 Midstream & Marketing Natural Gas Storage Forward Sales Contracts DTH	Mar. 31, 2013 Midstream & Marketing Natural Gas Storage Forward Sales Contracts DTH
Derivative
Outstanding derivative commodity instruments volumes				121,900,000	129,400,000										9,000,000	10,000,000	207,000,000	403,200,000	47,400,000	47,500,000	435,100,000	261,000,000	603,100,000	1,034,400,000	346,100,000	449,900,000	0	0	69,900,000	17,300,000	100,000	400,000
Maximum length of time hedged in price risk cash flow hedges (in months)				23 months								36 months			11 months		8 months
Derivative Liability, Fair Value, Gross Liability	$ 65.3	$ 57.5	$ 87.1														$ (0.4)	$ 5.5
Minimum approximate range of estimated dollar-denominated purchases of LPG (as a percent)												15.00%
Weighted Average Length if Time Hedged (in months)				7 months								17 months
Notional amount								439.8	441.2	0	173.0	199.4	92.7	52.0
Maximum approximate range of estimated dollar-denominated purchases of LPG (as a percent)												30.00%
Net losses associated with commodity price risk hedges expected to be reclassified into earnings during the next twelve months	12.3
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	4.1
Restricted cash	4.4	8.3	2.8			4.4	2.8
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	$ 0