Income Taxes - U.S. and foreign income (loss) from continuing operations before income taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Abstract]
Income (loss) before taxes - United States	$ (3,587)	$ 4,704	$ 2,867
Income Loss Before Income Taxes Foreign	447	4,820	7,106
Income (loss) before income taxes	(3,140)	9,524	9,973
Federal statutory income tax	(659)	2,000	2,095
Non-U.S. effective tax rates	194	1,399	1,766
Tax Legislation	0	0	(10)
Australia disposition	(349)	0	0
U.K. disposition	0	(732)	(150)
Recovery of outside basis	(22)	(77)	(21)
Adjustment to tax reserves, amount	18	9	(4)
Adjustment to valuation allowances	460	(225)	(26)
State income tax	(112)	123	135
Enhanded oil recovery credit	(6)	(27)	(99)
Malaysia Deepwater TaxCredits Incentive	0	(164)	0
Other	(9)	(39)	(18)
Total provision (benefit) for income taxes	$ (485)	$ 2,267	$ 3,668
Income (loss) before income taxes, United States, Percentage	114.20%	49.40%	28.70%
Income (loss) before income taxes, foreign, percentage	(14.20%)	50.60%	71.30%
Income (Loss) Before Income Taxes In Percent	100.00%	100.00%	100.00%
Federal statutory rate percentage	21.00%	21.00%	21.00%
Tax legislation, percentage	0.00%	0.00%	(0.10%)
Canada disposition, percentage	11.10%	0.00%	0.00%
U.K. disposition, percentage	0.00%	(7.70%)	(1.50%)
Recovery of outside basis, percentage	0.70%	(0.80%)	(0.20%)
Adjustment to valuation allowances	(14.60%)	(2.40%)	(0.30%)
State income tax, percentage	3.60%	1.30%	1.40%
Enhanced oil recovery, percentage	0.20%	(0.30%)	(1.00%)
Other, percentage	0.30%	(0.40%)	(0.20%)
Adjustment to tax reserves, percentage	(0.60%)	0.10%	0.00%
Effective Income Tax Rate, Continuing Operations, percetage	15.50%	23.80%	36.80%
Malaysia Deepwater Tax Credits Incentive, Percentage	0.00%	(1.70%)	0.00%
Non US effective tax rates percentage	(6.20%)	14.70%	17.70%