Supplemental Oil and Gas Disclosures (Unaudited) (Details 5) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Principal sources of change in the discounted future net cash flows
Sales, net of production costs	$ (13,152)	$ (9,152)	$ (5,943)
Net change in prices and production costs	12,167	13,006	7,650
Discoveries and improved recovery, net of related costs	6,751	5,147	1,718
Change in future development costs	(2,250)	(1,637)	(447)
Previously estimated development costs incurred during the period	2,479	1,355	1,685
Revision of quantities	(1,475)	(1,905)	(1,258)
Purchases of minerals in-place	2,139	7,794	530
Accretion of discount	4,161	2,439	1,054
Change in income taxes	(4,303)	(4,535)	823
Sales of properties	(1,285)	(3)
Change in production rates and other	273	182	(1,009)
Change in the discounted future net cash flows, total	$ 5,505	$ 12,691	$ 4,803