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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at fiscal year-end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, and unrealized gains and losses on certain investments in debt and equity securities as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
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-Section 04
-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Statement of Financial Accounting Standard (FAS)
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Risk Management (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Energy Commodity Price Risk Management [Abstract]
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	$ (1.8)	$ 7.8	$ (1.9)	$ 14.1
Amount of gain/(loss) reclassified from Accumulated OCI into income (effective portion)	(86.8)	(39.5)	139.8	(87.0)
Accumulated other comprehensive loss	96.8		96.8		186.4
Amount included in accumulated other comprehensive income associated with energy commodity price risk management activities			265.5		307.1
Amount of unrealized loss associated with energy commodity price risk management expected to be reclassified to earnings in next twelve months	171.5		171.5
Maximum length of time of exposure in commodity hedges			December 2015
Asset derivatives [Abstract]
Fair value of asset derivatives designated as hedging contracts	330.2		330.2		280.8
Fair value of asset derivatives not designated as hedging contracts	1.9		1.9		3.9
Total asset derivatives	332.1		332.1		284.7
Liability derivatives [Abstract]
Fair value of liability derivatives designated as hedging contracts	392.2		392.2		448.1
Fair value of liability derivatives not designated as hedging contracts	1.4		1.4		5.6
Total liability derivatives	393.6		393.6		453.7
Unamortized premium from early termination of interest rate swap agreements	435.3		435.3		456.5
Approximate weighted average amortization period on unamortized premium			16.9Y
Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Line Items]
Amount of gain recognized in income on derivative and on related hedged items	128.2	348.6	64.3	414.2
Amount of loss recognized in income on derivative and on related hedged items	(128.2)	(348.6)	(64.3)	(414.2)
Amount of gain/(loss) recognized in income on derivative and on related hedged items		0.1		0.8
Amount of gain/(loss) recognized in OCI on derivative (effective portion)	164.6	143.1	(97.8)	167.7
Amount of gain/(loss) reclassified from Accumulated OCI into income (effective portion)	(86.8)	(39.5)	139.8	(87.0)
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	(1.8)	7.8	(1.9)	14.1
Interest Rate Risk Management [Abstract]
Notional amount of interest rate swap agreements	5,275		5,275		4,775
Maximum length of time of exposure in interest rate hedges	2038-01-15		2038-01-15
Number of additional fixed-to-variable interest rate swap agreements			4
Notional amount of additional interest rate swap agreements			500
Crude oil (MMBbl) [Member]
Derivative [Line Items]
Net open position long/(short)	(24.2)		(24.2)
Natural gas fixed price (Bcf) [Member]
Derivative [Line Items]
Net open position long/(short)	(28.5)		(28.5)
Natural gas basis designated as hedge (Bcf) [Member]
Derivative [Line Items]
Net open position long/(short)	(28.5)		(28.5)
Natural gas basis not designated as hedge (Bcf) [Member]
Derivative [Line Items]
Net open position long/(short)	(5.2)		(5.2)
Natural gas fixed price not designated as hedge (Bcf) [Member]
Derivative [Line Items]
Net open position long/(short)	(0.1)		(0.1)
Energy commodity derivative contracts [Member] \| Cash Flow Hedging [Member] \| Other comprehensive income [Member]
Energy Commodity Price Risk Management [Abstract]
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)				13.3
Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Line Items]
Amount of gain/(loss) recognized in OCI on derivative (effective portion)	164.6	143.1	(97.8)
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)				13.3
Energy commodity derivative contracts [Member] \| Cash Flow Hedging [Member] \| Revenues-natural gas sales [Member]
Energy Commodity Price Risk Management [Abstract]
Amount of gain/(loss) reclassified from Accumulated OCI into income (effective portion)	0.1	1.7	1.0	1.7
Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Line Items]
Amount of gain/(loss) reclassified from Accumulated OCI into income (effective portion)	0.1	1.7	1.0	1.7
Energy commodity derivative contracts [Member] \| Cash Flow Hedging [Member] \| Revenues-product sales and other [Member]
Energy Commodity Price Risk Management [Abstract]
Amount of gain/(loss) reclassified from Accumulated OCI into income (effective portion)	(87.0)	(48.4)	(152.2)	(98.4)
Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Line Items]
Amount of gain/(loss) reclassified from Accumulated OCI into income (effective portion)	(87.0)	(48.4)	(152.2)	(98.4)
Energy commodity derivative contracts [Member] \| Cash Flow Hedging [Member] \| Gas purchases and other costs of sales [Member]
Energy Commodity Price Risk Management [Abstract]
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)		(0.1)		0.8
Amount of gain/(loss) reclassified from Accumulated OCI into income (effective portion)	0.1	7.2	11.4	9.7
Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Line Items]
Amount of gain/(loss) reclassified from Accumulated OCI into income (effective portion)	0.1	7.2	11.4	9.7
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)		(0.1)		0.8
Energy commodity derivative contracts [Member] \| Cash Flow Hedging [Member] \| Revenues [Member]
Energy Commodity Price Risk Management [Abstract]
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	(1.8)	7.9	(1.9)
Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Line Items]
Amount of gain/(loss) recognized in income on derivative and on related hedged items				0.8
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	(1.8)	7.9	(1.9)
Energy commodity derivative contracts [Member] \| Gas purchases and other costs of sales [Member]
Energy Commodity Price Risk Management [Abstract]
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	0.1
Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Line Items]
Amount of gain/(loss) recognized in income on derivative and on related hedged items		0.1	0.1
Amount of gain/(loss) recognized in OCI on derivative (effective portion)				167.7
Amount of gain/(loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)	0.1
Energy commodity derivative contracts [Member] \| Current [Member]
Asset derivatives [Abstract]
Fair value of asset derivatives designated as hedging contracts	29.9		29.9		20.1
Fair value of asset derivatives not designated as hedging contracts	1.9		1.9		3.9
Liability derivatives [Abstract]
Fair value of liability derivatives designated as hedging contracts	207.7		207.7		275.9
Fair value of liability derivatives not designated as hedging contracts	1.4		1.4		5.6
Energy commodity derivative contracts [Member] \| Noncurrent [Member]
Asset derivatives [Abstract]
Fair value of asset derivatives designated as hedging contracts	29.5		29.5		43.1
Liability derivatives [Abstract]
Fair value of liability derivatives designated as hedging contracts	126.4		126.4		103.0
Energy commodity derivative contracts [Member] \| Subtotal derivative [Member]
Asset derivatives [Abstract]
Fair value of asset derivatives designated as hedging contracts	59.4		59.4		63.2
Fair value of asset derivatives not designated as hedging contracts	1.9		1.9		3.9
Liability derivatives [Abstract]
Fair value of liability derivatives designated as hedging contracts	334.1		334.1		378.9
Fair value of liability derivatives not designated as hedging contracts	1.4		1.4		5.6
Interest rate swap agreements [Member] \| Fair Value Hedging [Member] \| Interest, net-income/expense [Member]
Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Line Items]
Amount of gain recognized in income on derivative and on related hedged items	128.2	348.6	64.3	414.2
Amount of loss recognized in income on derivative and on related hedged items	(128.2)	(348.6)	(64.3)	(414.2)
Interest rate swap agreements [Member] \| Current [Member]
Asset derivatives [Abstract]
Fair value of asset derivatives designated as hedging contracts	8.0		8.0
Interest rate swap agreements [Member] \| Noncurrent [Member]
Asset derivatives [Abstract]
Fair value of asset derivatives designated as hedging contracts	262.8		262.8		217.6
Liability derivatives [Abstract]
Fair value of liability derivatives designated as hedging contracts	58.1		58.1		69.2
Interest rate swap agreements [Member] \| Subtotal derivative [Member]
Asset derivatives [Abstract]
Fair value of asset derivatives designated as hedging contracts	270.8		270.8		217.6
Asset Position [Member]
Derivative Credit Risk [Line Items]
Interest rate swap agreements	270.8		270.8
Energy commodity derivative contracts	61.3		61.3
Gross exposure	332.1		332.1
Netting agreement impact	(42.1)		(42.1)
Net exposure	290.0		290.0
Margin Deposits Given To Held From Counterparties	1.2		1.2		2.4
Two Notches Decrease In Credit Rating [Member]
Additional Collateral Obligations [Line Items]
Incremental obligations	54.0		54.0
Cumulative obligations	$ 54.0		$ 54.0