Derivatives and Financial Instruments (Summary of Gains/(Losses) From Commodity Derivatives) (Details) - Commodity Derivatives - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) from commodity derivative activity	$ 1,123	$ (319)
Sales and other operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) from commodity derivative activity	679	(177)
Other income
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) from commodity derivative activity	3	13
Purchased crude oil and products
Derivative Instruments, Gain (Loss) [Line Items]
Net gain (loss) from commodity derivative activity	$ 441	$ (155)