Segment Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment	2
Revenues from contracts with customers	$ 5,063	$ 5,902	$ 4,247
Net loss on commodity derivatives	(72)	(14)	(36)
Income from equity method investments	87	225	256
Net gain (loss) on disposal of assets and other income			58
Net gain on disposal of assets	50	319	58
Other income	62	150	78
Production	712	842	716
Results of Operations, Transportation Costs	605	575	431
Exploration	149	289	409
Depreciation, depletion and amortization	2,397	2,441	2,372
Impairment of Oil and Gas Properties	24	75	229
Taxes other than income	311	299	183
General and Administrative Expense	356	394	371
Net interest and other	244	226	270
Net settlement loss	3	(14)	(19)
Loss on early extinguishment of debt	3	0	51
Provision (benefit) for income taxes	(88)	331	376
Income (loss) from continuing operations	480	1,096	(830)
Net Income (Loss) Attributable to Parent	480	1,096	(5,723)
Assets	20,245	21,321	22,012
Property, Plant and Equipment, Additions	2,591	2,685	2,150
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	0	0	47
United States Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues from contracts with customers	4,602	4,886
International Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues from contracts with customers	461	1,016
United States
Segment Reporting Information [Line Items]
Net settlement loss	(12)	(18)	(28)
Pension Plan [Member]
Segment Reporting Information [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment			32
Interest Rate Swap [Member]
Segment Reporting Information [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax			46
Operating Segments [Member] | United States Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues from contracts with customers	4,602	4,886	3,093
Net loss on commodity derivatives	52	(281)	45
Income from equity method investments	0	0	0
Net gain (loss) on disposal of assets and other income			1
Net gain on disposal of assets	0	0
Other income	13	16	12
Production	588	625	476
Results of Operations, Transportation Costs	561	499
Other Cost and Expense, Operating			354
Exploration	149	246	154
Depreciation, depletion and amortization	2,250	2,217	2,011
Impairment of Oil and Gas Properties	0	0	4
Taxes other than income	311	301	173
General and Administrative Expense	127	146	119
Net interest and other	0	0	0
Net settlement loss	0	0	0
Provision (benefit) for income taxes	6	(21)	1
Income (loss) from continuing operations		608	(148)
Net Income (Loss) Attributable to Parent	675
Assets	17,781	17,321	16,863
Property, Plant and Equipment, Additions	2,550	2,620	2,081
Operating Segments [Member] | International Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues from contracts with customers	461	1,016	1,154
Net loss on commodity derivatives	0	0	0
Income from equity method investments	87	225	256
Net gain (loss) on disposal of assets and other income			0
Net gain on disposal of assets	0	0
Other income	9	12	6
Production	126	215	239
Results of Operations, Transportation Costs	26	70
Other Cost and Expense, Operating			77
Exploration	0	3	5
Depreciation, depletion and amortization	121	197	328
Impairment of Oil and Gas Properties	0	0	0
Taxes other than income	0	0	0
General and Administrative Expense	25	32	30
Net interest and other	0	0	0
Net settlement loss	3	9	8
Provision (benefit) for income taxes	29	272	372
Income (loss) from continuing operations		473	374
Net Income (Loss) Attributable to Parent	233
Assets	1,530	2,083	4,201
Property, Plant and Equipment, Additions	16	39	42
Not Allocated to Segments [Member]
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0	0	0
Net loss on commodity derivatives	(124)	267	(81)
Income from equity method investments	0	0	0
Net gain (loss) on disposal of assets and other income			57
Net gain on disposal of assets	50	319
Other income	40	122	60
Production	(2)	2	1
Results of Operations, Transportation Costs	18	6
Other Cost and Expense, Operating			0
Exploration	0	40	250
Depreciation, depletion and amortization	26	27	33
Impairment of Oil and Gas Properties	24	75	225
Taxes other than income	0	(2)	10
General and Administrative Expense	204	216	222
Net interest and other	244	226	(270)
Net settlement loss	0	(23)	(27)
Loss on early extinguishment of debt	3		51
Provision (benefit) for income taxes	(123)	80	3
Income (loss) from continuing operations		15	(1,056)
Net Income (Loss) Attributable to Parent	(428)
Assets	934	1,917	948
Property, Plant and Equipment, Additions	25	26	27
Reclassification out of Accumulated Other Comprehensive Income [Member]
Segment Reporting Information [Line Items]
Net gain on disposal of assets	68	0
Net interest and other	(1)	0
Net settlement loss	6	(14)
Net Income (Loss) Attributable to Parent	75	(14)
Net settlement loss, net of tax | Reclassification out of Accumulated Other Comprehensive Income [Member]
Segment Reporting Information [Line Items]
Net settlement loss	(12)	(21)
Marketing revenues
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0	0	162
Marketing, including purchases from related parties	$ 0	$ 0	168
Marketing revenues | Operating Segments [Member] | United States Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues from contracts with customers			29
Marketing, including purchases from related parties			36
Marketing revenues | Operating Segments [Member] | International Exploration and Production [Member]
Segment Reporting Information [Line Items]
Revenues from contracts with customers			133
Marketing, including purchases from related parties			132
Marketing revenues | Not Allocated to Segments [Member]
Segment Reporting Information [Line Items]
Revenues from contracts with customers			0
Marketing, including purchases from related parties			$ 0