Acquisitions and Divestitures (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended							3 Months Ended				3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Sendero [Member]	Mar. 31, 2014 Gaines Dawson [Member]	Mar. 31, 2013 West Panhandle [Member]	Mar. 31, 2014 Lease Contract through Year 2 [Member]	Mar. 31, 2014 Lease Contract for Year 3 [Member]	Mar. 31, 2014 Discontinued Operations [Member]	Mar. 31, 2013 Discontinued Operations [Member]	Mar. 31, 2014 Discontinued Operations [Member] Pioneer Alaska [Member]	May 05, 2014 Discontinued Operations [Member] Pioneer Alaska [Member]	Mar. 31, 2014 Discontinued Operations [Member] Barnett Shale Field [Member]
Acquisitions and Divestitures [Line Items]
Gain on disposition of assets, net	$ 6	$ 24	$ 1	$ 3	$ 22
Proceeds from Divestiture of Interest in Consolidated Subsidiaries			31
Drilling rigs leased						12	8
Proceeds from Sale of Productive Assets	86	46		68	38
Impairment of oil and gas properties								111	0	97		14
Fair Value of Asset Group										253
Significant Acquisition and Disposal, Acquisition Costs or Sales Proceeds											$ 300