Asset Impairments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Oil and Gas Properties	$ 0	$ 0	$ 73	[1]	$ 137	[1]
South Raton (Deepwater Gulf of Mexico) [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Oil and Gas Properties	0	0	34		0
Piceance (Onshore US) [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Oil and Gas Properties	0	0	39		0
East Texas (Onshore US) [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Oil and Gas Properties	0	0	0		116
Other (Onshore US) [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Oil and Gas Properties	$ 0	$ 0	$ 0		$ 21

[1] See Note 4. Asset Impairments.