Derivative Instruments, Hedging Activities and Fair Value Measurements, Derivative Fair Value Amounts (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Derivatives designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 108.2		$ 155.4
Liability Derivatives	321.2		126.4
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	87.9		108.1
Liability Derivatives	290.7		31.7
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	43.7		30.3
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	44.2		77.8
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	163.6		5.5
Derivatives designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	127.1		26.2
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	20.3	[1]	47.3	[1]
Liability Derivatives	30.5	[1]	94.7	[1]
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	20.3		46.3
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0		1.0
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	30.3		93.0
Derivatives designated as hedging instruments [Member] | Commodity derivatives [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	0.2		1.7
Derivatives not designated as hedging instruments [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	47.0		43.4
Liability Derivatives	55.2		68.6
Derivatives not designated as hedging instruments [Member] | Interest rate derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0		0
Liability Derivatives	20.7		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	10.1		21.0
Derivatives not designated as hedging instruments [Member] | Interest rate derivatives [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	10.6		0.9
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	47.0		43.1
Liability Derivatives	34.5		46.6
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	34.4		38.6
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	12.6		4.5
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member] | Other current liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	32.5		41.2
Derivatives not designated as hedging instruments [Member] | Commodity derivatives [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	2.0		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		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.