Disclosures About Derivative Instruments and Hedging Activities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Designated as Hedging Instrument [Member] | LPG (millions of gallons) [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	236,700,000	231,900,000	236,700,000	231,900,000
Designated as Hedging Instrument [Member] | Natural gas (millions of dekatherms) [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	19,400,000	21,200,000	19,400,000	21,200,000
Designated as Hedging Instrument [Member] | Electricity (millions of kilowatt-hours) [Member] | Forward Purchase Contracts [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	927,200,000	1,688,400,000	927,200,000	1,688,400,000
Designated as Hedging Instrument [Member] | Electricity (millions of kilowatt-hours) [Member] | Forward Sales Contracts [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	451,000,000	131,800,000	451,000,000	131,800,000
Cash Flow Hedges [Member]
Derivative [Line Items]
Derivative Instruments Gain Loss Recognized in Other Comprehensive Income and Noncontrolling Interests Effective Portion	$ (9.1)	$ (72.8)	$ (6.5)	$ (192.4)
Interest Rate Contracts [Member] | Cash Flow Hedges [Member] | Interest Expense/Other Income [Member]
Derivative [Line Items]
Derivative Instruments Gain Loss Recognized in Other Comprehensive Income and Noncontrolling Interests Effective Portion	$ 14.0	$ (16.6)	$ 23.0	$ (29.0)