Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Revenues	$ 684	$ 651	$ 522	$ 579	$ 687	$ 749	$ 764	$ 933	$ 2,436	$ 3,133	$ 4,038
Depreciation, depletion and amortization expense									436	1,091	942
Impairment of natural gas and oil properties	0	817	470	1,034	2,576	2,839	1,535		2,321	6,950
Operating income (loss)	122	$ (725)	$ (492)	$ (1,100)	(2,561)	$ (2,842)	$ (1,284)	$ 165	(2,195)	(6,522)	1,373
Interest expense									88	56	59
Gain (loss) on derivatives									(339)	47	139
Loss on Early Extinguishment of Debt									(51)
Other income (loss), net									1	(30)	(4)
Provision (benefit) for income taxes									(29)	(2,005)	525
Assets	7,076				8,086				7,076	8,086	14,915
Capital investments									648	2,437	7,447
Restructuring charges									78
Cash and cash equivalents	1,423				15				1,423	15	53	$ 23
Change in accrued expenditures									(43)	33	(155)
Gain on sale of assets, net										283
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									(1,546)	(2,060)	(3,182)
Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues									1,435	2,095	2,850
Depreciation, depletion and amortization expense									371	1,028	884
Impairment of natural gas and oil properties									2,321	6,950
Operating income (loss)									(2,404)	(7,104)	1,013
Interest expense									87	47	47
Gain (loss) on derivatives									(338)	51	142
Other income (loss), net									5	(21)	(3)
Provision (benefit) for income taxes									(29)	(2,273)	402
Assets	4,178				6,588				4,178	6,588	13,018
Capital investments									623	2,258	7,254
Restructuring and other one-time charges									86
Exploration and Production [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									22	21	(12)
Midstream Services [Member]
Segment Reporting Information [Line Items]
Revenues									1,001	1,038	1,188
Depreciation, depletion and amortization expense									65	62	58
Operating income (loss)									209	583	361
Interest expense									1	9	12
Gain (loss) on derivatives									(1)		(1)
Other income (loss), net									(2)	(9)	(1)
Provision (benefit) for income taxes										268	123
Assets	1,331				1,290				1,331	1,290	1,554
Capital investments									21	167	144
Restructuring charges									3
Gain on sale of assets, net										277
Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									(1,568)	(2,081)	(3,170)
Other [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization expense										1
Operating income (loss)										(1)	(1)
Gain (loss) on derivatives										(4)	(2)
Loss on Early Extinguishment of Debt									(51)
Other income (loss), net									(2)
Assets	$ 1,567				$ 208				1,567	208	343
Capital investments									4	12	49
Marketing [Member] | Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues									$ (1,300)	$ (1,800)	$ (2,800)