Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 749	$ 928	$ 2,446	$ 3,076
Operating income (loss)	(2,842)	286	(3,961)	1,088
Other income, net			2	1
Gain (loss) on derivatives	15	78	30	(29)
Depreciation, depletion and amortization	275	238	876	$ 693
Impairment of natural gas and oil properties	2,839		4,374
Interest expense		13	52	$ 39
Provision (benefit) for income taxes	(1,088)	140	(1,532)	409
Assets	10,725	9,177	10,725	9,177	$ 14,925
Capital investments	468	574	2,054	1,837
Change in accrued expenditures	6	53	(5)	114
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(486)	(710)	(1,639)	(2,450)
Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues	491	652	1,647	2,169
Operating income (loss)	(2,910)	189	(4,471)	817
Other income, net			2	1
Gain (loss) on derivatives	15	79	32	(27)
Depreciation, depletion and amortization	255	223	824	650
Impairment of natural gas and oil properties	2,839		4,374
Interest expense		10	45	29
Provision (benefit) for income taxes	(1,112)	107	(1,724)	309
Assets	9,159	7,461	9,159	7,461
Capital investments	461	531	1,880	1,706
Exploration and Production [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	3	(3)	14	(13)
Exploration and Production [Member] | Canada [Member]
Segment Reporting Information [Line Items]
Assets	69	78	69	78
Midstream Services [Member]
Segment Reporting Information [Line Items]
Revenues	258	276	798	907
Operating income (loss)	68	97	511	272
Gain (loss) on derivatives				(1)
Depreciation, depletion and amortization	20	15	52	43
Interest expense		2	7	9
Provision (benefit) for income taxes	24	34	193	101
Assets	1,329	1,494	1,329	1,494
Capital investments	7	34	164	109
Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(489)	(707)	(1,653)	(2,437)
Other [Member]
Segment Reporting Information [Line Items]
Revenues			1
Operating income (loss)			(1)	(1)
Gain (loss) on derivatives		(1)	(2)	(1)
Interest expense		1		1
Provision (benefit) for income taxes		(1)	(1)	(1)
Assets	237	222	237	222
Capital investments		9	10	22
Marketing [Member] | Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	$ (414)	$ (612)	(1,400)	$ (2,200)
WPX and Statoil Property Acquisitions [Member] | Exploration and Production [Member]
Segment Reporting Information [Line Items]
Capital investments			516
WPX Property Acquisition [Member] | Midstream Services [Member]
Segment Reporting Information [Line Items]
Capital investments			$ 119