Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Basic and Diluted Earnings Per Share [Abstract]
Net Income (loss)	$ (296)	[1]	$ 441	[1]	$ 294	[1]	$ 14	[1]	$ 52	[2]	$ 232	[2]	$ 204	[2]	$ 237	[2]	$ 453	[1]	$ 725	[2]	$ (131)
Weighted Average Number of Shares Outstanding, Basic (in shares)																	176		175		173
Incremental Shares from Assumed Conversion of Dilutive Options and Restricted Stock (in shares)																	3		2		0
Weighted Average Number of Shares Outstanding, Diluted (in shares)																	179		177		173
Earnings Per Share, Basic (in dollars per share)	$ (1.67)	[1],[3]	$ 2.50	[1],[3]	$ 1.66	[1],[3]	$ 0.08	[1],[3]	$ 0.29	[2],[3]	$ 1.33	[2],[3]	$ 1.17	[2],[3]	$ 1.36	[2],[3]	$ 2.57	[1],[3]	$ 4.15	[2],[3]	$ (0.75)
Earnings Per Share, Diluted (in dollars per share)	$ (1.67)	[1],[3],[4]	$ 2.39	[1],[3],[4]	$ 1.61	[1],[3],[4]	$ 0.08	[1],[3],[4]	$ 0.29	[2],[3]	$ 1.31	[2],[3]	$ 1.10	[2],[3]	$ 1.34	[2],[3]	$ 2.54	[1],[3],[4]	$ 4.10	[2],[3]	$ (0.75)
Antidilutive stock options and shares of restricted stock																	2		2		4
Weighted average option exercise price per share (in dollars per share)	$ 85.40								$ 74.01								$ 85.40		$ 74.01		$ 60.40
Incremental stock options and shares of restricted stock excluded from calculation of diluted earnings in loss period																	0		0		2

[1] First quarter 2011 included the following: $8 million asset impairment charges (See Note 4. Asset Impairments); and $286 million loss on commodity derivative instruments, including unrealized mark-to-market loss of $303 million (See Note 10. Derivative Instruments and Hedging Activities). Second quarter 2011 included the following: $143 million gain on commodity derivative instruments, including unrealized mark-to-market gain of $142 million (See Note 10. Derivative Instruments and Hedging Activities); $25 million pre-tax gain on divestitures due to the completed transfer of assets and exit from Ecuador (See Note 3. Acquisitions and Divestitures); and $131 million asset impairment charges (See Note 4. Asset Impairments). Third quarter 2011 included the following: $322 million gain on commodity derivative instruments, including unrealized mark-to-market gain of $300 million (See Note 10. Derivative Instruments and Hedging Activities). Fourth quarter 2011 included the following: $620 million asset impairment charges (See Note 4. Asset Impairments); and $137 million loss on commodity derivative instruments, including unrealized mark-to-market loss of $162 million (See Note 10. Derivative Instruments and Hedging Activities).

[2] First quarter 2010 included the following: $145 million gain on commodity derivative instruments, including unrealized mark-to-market gain of $147 million (See Note 10. Derivative Instruments and Hedging Activities). Second quarter 2010 included the following: $96 million gain on commodity derivative instruments, including unrealized mark-to-market gain of $63 million (See Note 10. Derivative Instruments and Hedging Activities); and $26 million rig contract termination expense due to the Deepwater Moratorium. Third quarter 2010 included the following: $38 million gain on commodity derivative instruments, including unrealized mark-to-market gain of $5 million (See Note 10. Derivative Instruments and Hedging Activities); $114 million gain on sale of non-core onshore US assets (See Note 3. Acquisitions and Divestitures); and $100 million asset impairment charges (See Note 4. Asset Impairments). Fourth quarter 2010 included the following: $122 million loss on commodity derivative instruments, including unrealized mark-to-market loss of $145 million (See Note 10. Derivative Instruments and Hedging Activities); and $44 million asset impairment charges (See Note 4. Asset Impairments).

[3] The sum of the individual quarterly earnings (loss) per share amounts may not agree with year-to-date earnings per share as each quarterly computation is based on the income or loss for that quarter and the weighted average number of shares outstanding during that quarter.

[4] Consistent with GAAP, when dilutive, deferred compensation gains or losses, net of tax, are excluded from net income while the NBL shares held in the rabbi trust are included in the diluted share count. For this reason, the diluted earnings per share calculations for the three months ended June 30 and September 30, 2011 exclude deferred compensation gains of $4 million and $12 million, respectively, net of tax, and for the three months ended June 30, 2010 excludes a deferred compensation gain of $9 million, net of tax.