Financial and Derivative Instruments - Effect of Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Consolidated Statement of Income: The Effect of Derivatives not Designated as Hedging Instruments
Pre-tax deferred losses	$ 2	$ 0	$ 2	$ 0
Commodity
Consolidated Statement of Income: The Effect of Derivatives not Designated as Hedging Instruments
Effect of derivatives, gain (loss), net	(285)	(239)	(601)	218
Commodity | Sales and other operating revenues
Consolidated Statement of Income: The Effect of Derivatives not Designated as Hedging Instruments
Effect of derivatives, gain (loss), net	(268)	(216)	(542)	245
Commodity | Purchased crude oil and products
Consolidated Statement of Income: The Effect of Derivatives not Designated as Hedging Instruments
Effect of derivatives, gain (loss), net	(21)	(20)	(24)	(24)
Commodity | Other income
Consolidated Statement of Income: The Effect of Derivatives not Designated as Hedging Instruments
Effect of derivatives, gain (loss), net	$ 4	$ (3)	$ (35)	$ (3)