Revenues and Segment Information, Geographic Information by Country for Revenue and Long-Lived Assets (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2020		Sep. 30, 2020	[1],[2]	Jun. 30, 2020	[2]	Mar. 31, 2020	[2]	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Operating Revenues by Geographic Area
Revenues	$ 16,604	[1]	$ 15,809		$ 10,397		$ 22,102		$ 27,879	$ 27,249	$ 28,933	$ 24,263	$ 64,912	[3]	$ 108,324	[3]	$ 117,033	[3]
Geographic Information by Country for Long-Lived Assets
Long-lived assets	32,152								31,100				32,152		31,100
U.S. [Member]
Operating Revenues by Geographic Area
Revenues													45,174		77,173		82,992
Geographic Information by Country for Long-Lived Assets
Long-lived assets	28,184								27,485				28,184		27,485
Canada [Member]
Operating Revenues by Geographic Area
Revenues													4,294		7,915		9,211
Geographic Information by Country for Long-Lived Assets
Long-lived assets	1,877								1,886				1,877		1,886
U.K. and Ireland [Member]
Operating Revenues by Geographic Area
Revenues													9,268		13,584		15,208
Geographic Information by Country for Long-Lived Assets
Long-lived assets	1,353								1,232				1,353		1,232
Other Countries [Member]
Operating Revenues by Geographic Area
Revenues													6,176		9,652		$ 9,622
Mexico and Peru [Member]
Geographic Information by Country for Long-Lived Assets
Long-lived assets	$ 738								$ 497				$ 738		$ 497

[1] We recorded a charge of $326 million in September 2020 due to the expected liquidation of LIFO inventory layers as described in Note 5. We recognized a benefit of $102 million in December 2020 to adjust the $326 million estimate to the $224 million actual charge for the year ended December 31, 2020.

[2] The market value of our inventories accounted for under the LIFO method fell below their historical cost on an aggregate basis as of March 31, 2020. As a result, we recorded an LCM inventory valuation adjustment of $2.5 billion in March 2020 as described in Note 5. The market value of our LIFO inventories improved due to the subsequent recovery in market prices, which resulted in a reversal of $2.2 billion in the quarter ended June 30, 2020 and the remaining amount in the quarter ended September 30, 2020.

[3] Includes excise taxes on sales by certain of our international operations of $4,797 million, $5,595 million, and $5,626 million for the years ended December 31, 2020, 2019, and 2018.