Acquisitions and Divestitures (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Acquisitions and Divestitures [Line Items]
Gain (loss) on disposition of assets, net	$ 1		$ 6
Tangible asset impairment	6	[1]	0	[1]
Idle Rig Expense	23	[2]	0	[2]
Proceeds from Sale of Productive Assets	4		86
Impairment of oil and gas properties	138		0
Sendero [Member]
Acquisitions and Divestitures [Line Items]
Gain (loss) on disposition of assets, net			1
Proceeds from Divestiture of Interest in Consolidated Subsidiaries			31
Idle Rig Expense	9
Gaines Dawson [Member]
Acquisitions and Divestitures [Line Items]
Gain (loss) on disposition of assets, net			2
Proceeds from Sale of Productive Assets			72
Lease Contract through Year 2 [Member]
Acquisitions and Divestitures [Line Items]
Drilling rigs leased			12
Lease Contract for Year 3 [Member]
Acquisitions and Divestitures [Line Items]
Drilling rigs leased			8
Discontinued Operations [Member] | Hugoton field [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from Sale of Productive Assets					328
Discontinued Operations [Member] | Pioneer Alaska [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from Sale of Productive Assets					267
Discontinued Operations [Member] | Barnett Shale Field [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from Sale of Productive Assets					$ 150

[1] Represents charges to reduce excess material and supplies inventories to their market values. See Note D for additional information on the fair value of materials and supplies inventory.

[2] Primarily represents expenses attributable to idle drilling rig fees, which are not chargeable to joint operations.