Segment Information (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues from external customers	$ 745,000,000	$ 636,000,000	$ 667,000,000	$ 990,000,000	$ 1,175,000,000	$ 951,000,000	$ 816,000,000	$ 920,000,000	$ 3,038,000,000	$ 3,862,000,000	$ 3,203,000,000
Depreciation, depletion and amortization expense									471,000,000	560,000,000	504,000,000
Impairments									16,000,000	171,000,000	0
Operating income (loss)	64,000,000	$ (29,000,000)	$ 22,000,000	$ 213,000,000	352,000,000	$ 66,000,000	$ 124,000,000	$ 255,000,000	270,000,000	797,000,000	731,000,000
Interest expense									65,000,000	124,000,000	135,000,000
Gain (loss) on derivatives									274,000,000	(118,000,000)	422,000,000
Loss on early extinguishment of debt									8,000,000	(17,000,000)	(70,000,000)
Other income (loss), net									(7,000,000)	0	5,000,000
Provision (benefit) for income taxes									(411,000,000)	1,000,000	(93,000,000)
Assets	6,717,000,000				5,797,000,000				6,717,000,000	5,797,000,000	7,521,000,000
Capital investments									1,140,000,000	1,248,000,000	1,293,000,000
Restructuring charges									11,000,000	39,000,000	0
Cash and cash equivalents	5,000,000				201,000,000				5,000,000	201,000,000
Property plant and equipment	5,267,000,000				4,656,000,000				5,267,000,000	4,656,000,000
Unamortized debt expense	19,000,000				23,000,000				19,000,000	23,000,000
Operating lease assets	159,000,000								159,000,000
Derivative assets	278,000,000				130,000,000				278,000,000	130,000,000
Increase (decrease) in accrued expenditures between periods									34,000,000	(53,000,000)	0
Marketing
Segment Reporting Information [Line Items]
Revenues from external customers									1,297,000,000	1,222,000,000	972,000,000
Exploration and Production
Segment Reporting Information [Line Items]
Revenues from external customers									1,740,000,000	2,551,000,000	2,105,000,000
Depreciation, depletion and amortization expense											440,000,000
Marketing
Segment Reporting Information [Line Items]
Revenues from external customers									1,298,000,000	1,311,000,000	1,098,000,000
Depreciation, depletion and amortization expense											64,000,000
Operating Segments | Exploration and Production
Segment Reporting Information [Line Items]
Revenues from external customers									1,703,000,000	2,525,000,000	2,086,000,000
Depreciation, depletion and amortization expense									462,000,000	514,000,000
Impairments									13,000,000	15,000,000
Operating income (loss)									283,000,000	794,000,000	549,000,000
Interest expense									65,000,000	124,000,000	135,000,000
Gain (loss) on derivatives									274,000,000	(118,000,000)	421,000,000
Loss on early extinguishment of debt									0	0	0
Other income (loss), net									(9,000,000)	2,000,000	4,000,000
Provision (benefit) for income taxes									(411,000,000)	1,000,000	(93,000,000)
Assets	6,235,000,000				4,872,000,000				6,235,000,000	4,872,000,000	5,109,000,000
Capital investments									1,138,000,000	1,231,000,000	1,248,000,000
Restructuring charges									11,000,000	37,000,000
Operating Segments | Exploration and Production | Marketing
Segment Reporting Information [Line Items]
Revenues from external customers									0	0	0
Operating Segments | Marketing
Segment Reporting Information [Line Items]
Revenues from external customers									2,850,000,000	3,745,000,000	3,198,000,000
Depreciation, depletion and amortization expense									9,000,000	46,000,000
Impairments									3,000,000	155,000,000
Operating income (loss)									(13,000,000)	4,000,000	183,000,000
Interest expense									0	0	0
Gain (loss) on derivatives									0	0	1,000,000
Loss on early extinguishment of debt									0	0	0
Other income (loss), net									0	(2,000,000)	1,000,000
Provision (benefit) for income taxes									0	0	0
Assets	314,000,000				539,000,000				314,000,000	539,000,000	1,288,000,000
Capital investments									0	9,000,000	32,000,000
Restructuring charges										2,000,000
Operating Segments | Marketing | Non Core Gathering Assets
Segment Reporting Information [Line Items]
Impairments										10,000,000
Operating Segments | Marketing | Marketing
Segment Reporting Information [Line Items]
Revenues from external customers									2,849,000,000	3,497,000,000	2,867,000,000
Intersegment Revenues
Segment Reporting Information [Line Items]
Revenues from external customers									(1,515,000,000)	(2,408,000,000)	(2,081,000,000)
Intersegment Revenues | Marketing
Segment Reporting Information [Line Items]
Revenues from external customers									(1,552,000,000)	(2,275,000,000)	(1,895,000,000)
Intersegment Revenues | Exploration and Production
Segment Reporting Information [Line Items]
Revenues from external customers									37,000,000	26,000,000	19,000,000
Intersegment Revenues | Marketing
Segment Reporting Information [Line Items]
Revenues from external customers									(1,552,000,000)	(2,434,000,000)	(2,100,000,000)
Intersegment Revenues | Marketing | Marketing
Segment Reporting Information [Line Items]
Revenues from external customers									(1,600,000,000)	(2,300,000,000)	(1,900,000,000)
Other
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization expense									0	0	0
Impairments									0	1,000,000
Operating income (loss)									0	(1,000,000)	(1,000,000)
Interest expense									0	0	0
Gain (loss) on derivatives									0	0	0
Loss on early extinguishment of debt									8,000,000	(17,000,000)	(70,000,000)
Other income (loss), net									2,000,000	0	0
Provision (benefit) for income taxes									0	0	0
Assets	168,000,000				386,000,000				168,000,000	386,000,000	1,124,000,000
Capital investments									2,000,000	8,000,000	13,000,000
Cash and cash equivalents	5,000,000				205,000,000				5,000,000	205,000,000	914,000,000
Income taxes receivable	30,000,000				89,000,000				30,000,000	89,000,000	89,000,000
Property plant and equipment	27,000,000				60,000,000				27,000,000	60,000,000	95,000,000
Unamortized debt expense	11,000,000				11,000,000				11,000,000	11,000,000	5,000,000
Prepayments	8,000,000				8,000,000				8,000,000	8,000,000	11,000,000
Assets for non-qualified retirement plan	7,000,000				8,000,000				7,000,000	8,000,000	$ 10,000,000
Operating lease assets	$ 80,000,000								$ 80,000,000
Accounts receivable, net					4,000,000					4,000,000
Derivative assets					$ 1,000,000					$ 1,000,000