Derivatives and Financial Instruments - Summary of Gains/(Losses) From Commodity Derivatives (Details) - Commodity derivatives - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) from commodity derivative activity	$ 620	$ (278)	$ 113
Sales and other operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) from commodity derivative activity	436	(150)	192
Other income
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) from commodity derivative activity	10	33	(15)
Purchased crude oil and products
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) from commodity derivative activity	$ 174	$ (161)	$ (64)