Segment Information - Table (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating Revenues	$ 979	$ 1,177	$ 3,727	$ 2,610
Revenues	1,943	2,276	6,977	5,851
Income (Loss) Before Income Taxes	(17)	(1,214)	621	(4,058)
TOTAL ASSETS	11,981		11,981		$ 13,028
Scenario, Previously Reported [Member]
Segment Reporting Information [Line Items]
Income (Loss) Before Income Taxes		(1,154)		(3,825)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating Revenues	(1,030)	(1,025)	(3,200)	(2,656)
Intersegment Revenues	1,030	1,025	3,200	2,656
Revenues	0	0	0	0
Income (Loss) Before Income Taxes	0	(2)	(1)	(2)
TOTAL ASSETS	(387)		(387)		(398)
Intersegment Eliminations [Member] | Scenario, Previously Reported [Member]
Segment Reporting Information [Line Items]
Income (Loss) Before Income Taxes		(2)		(2)
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,943	2,276	6,977	5,851
Intersegment Revenues	0	0	0	0
Exploration And Production [Member]
Segment Reporting Information [Line Items]
Revenues	979	1,177	3,727	2,610
Exploration And Production [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenues	979	1,177	3,727	2,610
Intersegment Revenues	0	0	0	0
Income (Loss) Before Income Taxes	(14)	(642)	1,094	(3,465)
TOTAL ASSETS	10,451		10,451		11,249
Exploration And Production [Member] | Operating Segments [Member] | Scenario, Previously Reported [Member]
Segment Reporting Information [Line Items]
Income (Loss) Before Income Taxes		(710)		(3,360)
Marketing, Gathering And Compression [Member]
Segment Reporting Information [Line Items]
Revenues	964	1,099	3,250	3,241
Marketing, Gathering And Compression [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenues	1,994	2,124	6,450	5,897
Intersegment Revenues	(1,030)	(1,025)	(3,200)	(2,656)
Income (Loss) Before Income Taxes	7	(339)	(440)	(343)
TOTAL ASSETS	923		923		1,118
Marketing, Gathering And Compression [Member] | Operating Segments [Member] | Scenario, Previously Reported [Member]
Segment Reporting Information [Line Items]
Income (Loss) Before Income Taxes		(211)		(215)
Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Other Segments [Member] | Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	0	0	0	0
Intersegment Revenues	0	0	0	0
Income (Loss) Before Income Taxes	(10)	(231)	(32)	(248)
TOTAL ASSETS	$ 994		$ 994		$ 1,059
Other Segments [Member] | Corporate, Non-Segment [Member] | Scenario, Previously Reported [Member]
Segment Reporting Information [Line Items]
Income (Loss) Before Income Taxes		$ (231)		$ (248)