Segment Information (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment					2
Revenues from contracts with customers	$ 490		$ 1,381		$ 1,514	$ 2,581
Net gain (loss) on commodity derivatives	(70)		16		132	(75)
Income (loss) from equity method investments	(152)		31		(164)	42
Net gain (loss) on disposal of assets	(2)		(8)		7	34
Other income	6		13		13	48
Less costs and expenses:
Production	129		193		289	380
Shipping, handling and other operating	105		170		249	324
Exploration	26		26		54	85
Depreciation, depletion and amortization	597		605		1,241	1,159
Impairments	0		18		97	24
Taxes other than income	30		79		96	151
General and administrative	88		87		164	181
Net interest and other	69		64		133	113
Other net periodic benefit credit	(7)		(2)		(7)	(7)
Income tax provision (benefit)	(15)		32		(18)	(115)
Net income	(750)	$ (46)	161	$ 174	(796)	335
Assets	18,567		21,282		18,567	21,282	$ 20,245
Capital expenditures	139		701		707	1,315
Severance costs					13
Goodwill impairment loss					95	0
Pension Plan
Less costs and expenses:
Other net periodic benefit credit	14		2		16	2
Net curtailment gain	3		0		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	(96)		11		75	(102)
Income (loss) from equity method investments	(152)		0		(152)	0
Net gain (loss) on disposal of assets	(2)		(8)		7	34
Other income	1		7		2	38
Less costs and expenses:
Production	0		0		0	(2)
Shipping, handling and other operating	13		13		14	14
Exploration	0		0		0	0
Depreciation, depletion and amortization	6		6		12	12
Impairments			18		97	24
Taxes other than income	0		0		0	(2)
General and administrative	53		48		93	106
Net interest and other	69		64		133	113
Other net periodic benefit credit	(7)		(1)		(7)	(4)
Income tax provision (benefit)	(4)		12		(6)	(122)
Net income	(379)		(150)		(404)	(169)
Assets	632		830		632	830
Capital expenditures	2		5		9	8
Severance costs	13
Not Allocated to Segments | Pension Plan
Less costs and expenses:
Net curtailment gain	17				17
United States E&P
Segment Reporting Information [Line Items]
Revenues from contracts with customers	462		1,200		1,432	2,262
United States E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenues from contracts with customers	462		1,200		1,432	2,262
Net gain (loss) on commodity derivatives	26		5		57	27
Income (loss) from equity method investments	0		0		0	0
Net gain (loss) on disposal of assets	0		0		0	0
Other income	3		4		7	5
Less costs and expenses:
Production	114		147		257	286
Shipping, handling and other operating	91		147		231	287
Exploration	26		26		54	85
Depreciation, depletion and amortization	569		561		1,186	1,075
Impairments			0		0	0
Taxes other than income	30		79		96	153
General and administrative	32		31		64	60
Net interest and other	0		0		0	0
Other net periodic benefit credit	0		0		0	0
Income tax provision (benefit)	(6)		3		(7)	1
Net income	(365)		215		(385)	347
Assets	16,791		17,539		16,791	17,539
Capital expenditures	137		686		698	1,292
Int'l E&P
Segment Reporting Information [Line Items]
Revenues from contracts with customers			181			319
Int'l E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenues from contracts with customers	28		181		82	319
Net gain (loss) on commodity derivatives	0		0		0	0
Income (loss) from equity method investments	0		31		(12)	42
Net gain (loss) on disposal of assets	0		0		0	0
Other income	2		2		4	5
Less costs and expenses:
Production	15		46		32	96
Shipping, handling and other operating	1		10		4	23
Exploration	0		0		0	0
Depreciation, depletion and amortization	22		38		43	72
Impairments			0		0	0
Taxes other than income	0		0		0	0
General and administrative	3		8		7	15
Net interest and other	0		0		0	0
Other net periodic benefit credit	0		(1)		0	(3)
Income tax provision (benefit)	(5)		17		(5)	6
Net income	(6)		96		(7)	157
Assets	1,144		2,913		1,144	2,913
Capital expenditures	$ 0		$ 10		$ 0	$ 15