Segment Information (Details) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment							2
Revenues from contracts with customers	$ 1,249			$ 1,538			$ 3,830	$ 4,522
Net gain (loss) on commodity derivatives	47			(70)			(28)	(324)
Income from equity method investments	21			64			63	161
Net gain on disposal of assets	22			16			56	323
Other income	6			119			54	135
Less costs and expenses:
Production	163			215			543	637
Shipping, handling and other operating	138			152			462	408
Exploration	22			56			107	173
Depreciation, depletion and amortization	622			626			1,781	1,828
Impairments	0			8			24	50
Taxes other than income	81			86			232	215
General and administrative	82			101			263	306
Net interest and other	64			58			177	168
Other net periodic benefit costs	(2)			8			(9)	11
Income tax provision (benefit)	10			103			(105)	315
Net income	165	$ 161	$ 174	254	$ 96	$ 356	500	706
Capital expenditures	675			704			1,990	1,988
Pension Plan
Less costs and expenses:
Other net periodic benefit costs	0						2	16
Not Allocated to Segments
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0			0			0	0
Net gain (loss) on commodity derivatives	33			19			(69)	(69)
Income from equity method investments	0			0			0	0
Net gain on disposal of assets	22			16			56	323
Other income	1			113			39	121
Less costs and expenses:
Production	0			0			(2)	(1)
Shipping, handling and other operating	0			0			14	(1)
Exploration	0			0			0	0
Depreciation, depletion and amortization	8			6			20	20
Impairments				8			24	50
Taxes other than income	1			0			(1)	(3)
General and administrative	43			57			149	173
Net interest and other	64			58			177	168
Other net periodic benefit costs	(2)			11			(6)	18
Income tax provision (benefit)	0			71			(122)	84
Net income	(58)			(63)			(227)	(133)
Capital expenditures	7			7			15	17
United States E&P
Segment Reporting Information [Line Items]
Revenues from contracts with customers	1,172			1,347			3,434	3,693
United States E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenues from contracts with customers	1,172			1,347			3,434	3,693
Net gain (loss) on commodity derivatives	14			(89)			41	(255)
Income from equity method investments	0			0			0	0
Net gain on disposal of assets	0			0			0	0
Other income	3			2			8	7
Less costs and expenses:
Production	147			172			433	476
Shipping, handling and other operating	137			136			424	364
Exploration	22			55			107	170
Depreciation, depletion and amortization	589			571			1,664	1,655
Impairments				0			0	0
Taxes other than income	80			86			233	218
General and administrative	34			37			94	108
Net interest and other	0			0			0	0
Other net periodic benefit costs	0			0			0	0
Income tax provision (benefit)	0			2			1	5
Net income	180			201			527	449
Capital expenditures	667			691			1,959	1,943
Int'l E&P
Segment Reporting Information [Line Items]
Revenues from contracts with customers				191			396	829
Int'l E&P | Operating Segments
Segment Reporting Information [Line Items]
Revenues from contracts with customers	77			191			396	829
Net gain (loss) on commodity derivatives	0			0			0	0
Income from equity method investments	21			64			63	161
Net gain on disposal of assets	0			0			0	0
Other income	2			4			7	7
Less costs and expenses:
Production	16			43			112	162
Shipping, handling and other operating	1			16			24	45
Exploration	0			1			0	3
Depreciation, depletion and amortization	25			49			97	153
Impairments				0			0	0
Taxes other than income	0			0			0	0
General and administrative	5			7			20	25
Net interest and other	0			0			0	0
Other net periodic benefit costs	0			(3)			(3)	(7)
Income tax provision (benefit)	10			30			16	226
Net income	43			116			200	390
Capital expenditures	1			6			16	28
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plan Adjustment, Net Gain (Loss) Due To Settlement, Attributable To Parent [Member]
Less costs and expenses:
Other net periodic benefit costs	$ 0			$ 10			$ 2	$ 16