Segment Information (Details) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment							2
Revenues from contracts with customers	$ 761			$ 1,249			$ 2,275	$ 3,830
Net gain (loss) on commodity derivatives	(1)			47			131	(28)
Income (loss) from equity method investments	(10)			21			(174)	63
Net gain on disposal of assets	1			22			8	56
Other income	3			6			16	54
Less costs and expenses:
Production	129			163			418	543
Shipping, handling and other operating	183			138			432	462
Exploration	27			22			81	107
Depreciation, depletion and amortization	554			622			1,795	1,781
Impairments	1			0			98	24
Taxes other than income	49			81			145	232
General and administrative	53			82			217	263
Net interest and other	62			64			195	177
Other net periodic benefit costs	6			(2)			(1)	(9)
Income tax provision (benefit)	7			10			(11)	(105)
Net income (loss)	(317)	$ (750)	$ (46)	165	$ 161	$ 174	(1,113)	500
Assets	18,663			20,373			18,663	20,373	$ 20,245
Capital expenditures	177			675			884	1,990
Goodwill impairment loss							95	0
Severance costs							15
Pension Plan
Less costs and expenses:
Other net periodic benefit costs	9			0			25	2
Net curtailment gain							3	0
Not Allocated to Segments
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0			0			0	0
Net gain (loss) on commodity derivatives	(36)			33			39	(69)
Income (loss) from equity method investments	(18)			0			(170)	0
Net gain on disposal of assets	1			22			8	56
Other income	1			1			3	39
Less costs and expenses:
Production	0			0			0	(2)
Shipping, handling and other operating	28			0			42	14
Exploration	6			0			6	0
Depreciation, depletion and amortization	5			8			17	20
Impairments	1						98	24
Taxes other than income	1			1			1	(1)
General and administrative	25			43			118	149
Net interest and other	62			64			195	177
Other net periodic benefit costs	6			(2)			(1)	(6)
Income tax provision (benefit)	4			0			(2)	(122)
Net income (loss)	(190)			(58)			(594)	(227)
Assets	1,163			648			1,163	648
Capital expenditures	1			7			10	15
Not Allocated to Segments | Pension Plan
Less costs and expenses:
Net curtailment gain							17
United States E&P
Segment Reporting Information [Line Items]
Revenues from contracts with customers	722			1,172			2,154	3,434
United States E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenues from contracts with customers	722			1,172			2,154	3,434
Net gain (loss) on commodity derivatives	35			14			92	41
Income (loss) from equity method investments	0			0			0	0
Net gain on disposal of assets	0			0			0	0
Other income	1			3			8	8
Less costs and expenses:
Production	118			147			375	433
Shipping, handling and other operating	154			137			385	424
Exploration	21			22			75	107
Depreciation, depletion and amortization	530			589			1,716	1,664
Impairments	0						0	0
Taxes other than income	48			80			144	233
General and administrative	25			34			89	94
Net interest and other	0			0			0	0
Other net periodic benefit costs	0			0			0	0
Income tax provision (benefit)	(3)			0			(10)	1
Net income (loss)	(135)			180			(520)	527
Assets	16,396			17,722			16,396	17,722
Capital expenditures	176			667			874	1,959
Int'l E&P
Segment Reporting Information [Line Items]
Revenues from contracts with customers								396
Int'l E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenues from contracts with customers	39			77			121	396
Net gain (loss) on commodity derivatives	0			0			0	0
Income (loss) from equity method investments	8			21			(4)	63
Net gain on disposal of assets	0			0			0	0
Other income	1			2			5	7
Less costs and expenses:
Production	11			16			43	112
Shipping, handling and other operating	1			1			5	24
Exploration	0			0			0	0
Depreciation, depletion and amortization	19			25			62	97
Impairments	0						0	0
Taxes other than income	0			0			0	0
General and administrative	3			5			10	20
Net interest and other	0			0			0	0
Other net periodic benefit costs	0			0			0	(3)
Income tax provision (benefit)	6			10			1	16
Net income (loss)	8			43			1	200
Assets	1,104			2,003			1,104	2,003
Capital expenditures	$ 0			$ 1			$ 0	$ 16