Disclosures About Derivative Instruments and Hedging Activities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Electricity (millions of kilowatt-hours) [Member] | Forward Purchase Contracts [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	664,700,000	1,180,800,000
Electricity (millions of kilowatt-hours) [Member] | Forward Sales Contracts [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	371,000,000	195,300,000
Designated as Hedging Instrument [Member] | LPG (millions of gallons) [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	215,200,000	212,100,000
Cash Flow Hedges [Member]
Derivative [Line Items]
Derivative Instruments Gain Loss Recognized in Other Comprehensive Income and Noncontrolling Interests Effective Portion	$ 48.0	$ (6.8)
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	$ (1.7)	$ 1.0