Fair Value Measurements (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Fair Value - Other Financial Instruments
Debt fair value	$ 4,500,000,000	$ 5,500,000,000
Debt carrying value	4,200,000,000	5,100,000,000
Level 1
Fair value of assets and liabilities measured on recurring basis
Trading equity securities - natural resources industry	135,000,000	116,000,000
Trading U.S. treasury securities		10,000,000
Commodity derivatives assets	481,000,000	178,000,000
Total assets	616,000,000	304,000,000
Commodity derivative liabilities	377,000,000	201,000,000
Total liabilities	377,000,000	201,000,000
Level 2
Fair value of assets and liabilities measured on recurring basis
Commodity derivatives assets	608,000,000	797,000,000
Total assets	608,000,000	797,000,000
Commodity derivative liabilities	764,000,000	916,000,000
Total liabilities	764,000,000	916,000,000
Netting and Collateral
Fair value of assets and liabilities measured on recurring basis
Commodity derivatives assets	(801,000,000)	(680,000,000)
Total assets	(801,000,000)	(680,000,000)
Commodity derivative liabilities	(830,000,000)	(736,000,000)
Total liabilities	(830,000,000)	(736,000,000)
Total Fair Value
Fair value of assets and liabilities measured on recurring basis
Trading equity securities - natural resources industry	135,000,000	116,000,000
Trading U.S. treasury securities		10,000,000
Commodity derivatives assets	288,000,000	295,000,000
Total assets	423,000,000	421,000,000
Commodity derivative liabilities	311,000,000	381,000,000
Total liabilities	$ 311,000,000	$ 381,000,000

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Fair Value as of the balance sheet date of assets measured on a recurring basis.

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Fair Value as of the balance sheet date of liabilities measured on a recurring basis.

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- Definition

Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date before deducting unamortized discount or premiums (if any). May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number APB14-1
-Paragraph 31
-Subparagraph b

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
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-Paragraph 16
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Estimated fair value of the debt instrument at the balance-sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10

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The fair value as of the balance sheet date of firm holdings in debt obligations issued by the US government including short-term Treasury bills, medium-term Treasury notes, and long-term Treasury bonds, as well as debt issued by agencies. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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- Definition

Fair value as of the balance sheet date of price risk derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets on the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 17

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Fair value as of the balance sheet date of price risk derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities on the balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Paragraph 17

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Total common and preferred stock (which is neither mandatorily redeemable nor redeemable at the option of the holder) equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for equity securities formerly categorized as available-for-sale or held-to-maturity which the entity held as of the date it opted to account for such securities at fair value. An enterprise may also categorize such a security as trading without the intent to sell it in the near term assuming the decision to categorize the security as trading occurred at acquisition; this is the reason why the trading category of investments in debt securities are bought and sold "principally" for sale in the near term. Transfers into and out of the trading category should be rare. Such financial instruments that are held as of the reporting date are measured at fair value with unrealized holding gains and losses (the difference between fair value and the previously reported carrying amount) included in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 159
-Paragraph 29

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 13

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Implementation Guide (Q and A)
-Number FAS115
-Paragraph 35

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Paragraph 12
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