Segment Information (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 811	$ 522		$ 1,657	$ 1,101
Depreciation, depletion and amortization expense	123	107		229	250
Impairment of natural gas and oil properties		470	$ 1,034		1,504
Operating income (loss)	188	(492)		454	(1,592)
Interest expense	34	17		66	31
Gain (loss) on derivatives	134	(85)		250	(99)
Loss on Early Extinguishment of Debt	(10)			(11)
Other income (loss), net	6			8	(3)
Provision (benefit) for income taxes		(1)
Assets	7,150	7,377		7,150	7,377	$ 7,076
Capital investments	325	74		615	196
Restructuring charges		11			75
Cash and cash equivalents	1,111	998		1,111	998	$ 1,423	$ 15
Change in accrued expenditures	41	27		(11)	(51)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(537)	(321)		(1,112)	(699)
Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues	531	291		1,097	634
Depreciation, depletion and amortization expense	107	90		197	217
Impairment of natural gas and oil properties		470			1,504
Operating income (loss)	146	(549)		371	(1,709)
Interest expense	34	16		66	30
Gain (loss) on derivatives	134	(85)		250	(98)
Other income (loss), net	2	3		4	1
Provision (benefit) for income taxes		(1)
Assets	4,633	5,000		4,633	5,000
Capital investments	318	73		601	193
Restructuring charges		11			72
Exploration and Production [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	5	7		8	14
Midstream Services [Member]
Segment Reporting Information [Line Items]
Revenues	280	231		560	467
Depreciation, depletion and amortization expense	16	17		32	33
Operating income (loss)	42	57		83	117
Interest expense		1			1
Gain (loss) on derivatives					(1)
Other income (loss), net	4	(2)		4	(3)
Assets	1,281	1,227		1,281	1,227
Capital investments	6			12	2
Restructuring charges					3
Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(542)	(328)		(1,120)	(713)
Other [Member]
Segment Reporting Information [Line Items]
Loss on Early Extinguishment of Debt	(10)			(11)
Other income (loss), net		(1)			(1)
Assets	1,236	1,150		1,236	1,150
Capital investments	1	1		2	1
Cash and cash equivalents	1,100	998		1,100	998
Marketing [Member] | Midstream Services [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	$ (490)	$ (267)		$ (1,014)	$ (586)