Derivative Instruments, Hedging Activities and Fair Value Measurements, Derivative Fair Value Amounts (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 142.3		$ 155.4
Liability Derivatives	333.1		126.4
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	92.3		108.1
Liability Derivatives	263.7		31.7
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	44.3		30.3
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	48.0		77.8
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	152.0		5.5
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	111.7		26.2
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	50.0	[1]	47.3	[1]
Liability Derivatives	69.4	[1]	94.7	[1]
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	49.8		46.3
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.2		1.0
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	69.4		93.0
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	0		1.7
Derivatives not designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	36.3		43.4
Liability Derivatives	60.2		68.6
Derivatives not designated as hedging instruments [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0		0
Liability Derivatives	24.1		21.9
Derivatives not designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0		0
Derivatives not designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0		0
Derivatives not designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	11.2		21.0
Derivatives not designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	12.9		0.9
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	36.1		43.1
Liability Derivatives	36.1		46.6
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	29.3		38.6
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	6.8		4.5
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	33.2		41.2
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	2.9		5.4
Derivatives not designated as hedging instruments [Member] | Foreign currency derivatives [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.2		0.3
Derivatives not designated as hedging instruments [Member] | Foreign currency derivatives [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 0		$ 0.1

[1] Represents commodity derivative instrument transactions that have either not settled or have settled and not been invoiced. Settled and invoiced transactions are reflected in either accounts receivable or accounts payable depending on the outcome of the transaction.