Segment Information, Geographic Information by Country for Revenue and Long-Lived Assets (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	[2]	Jun. 30, 2016	[3]	Mar. 31, 2016	[4]	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Operating Revenues by Geographic Area
Operating revenues	$ 26,392	[1]	$ 23,562	$ 22,254	$ 21,772	$ 20,712	$ 19,649		$ 19,584		$ 15,714		$ 93,980	[5]	$ 75,659	[5]	$ 87,804	[5]
Geographic Information by Country for Long-Lived Assets
Long-lived assets	29,061					28,142							29,061		28,142
U.S. [Member]
Operating Revenues by Geographic Area
Operating revenues													66,614		51,479		60,319
Geographic Information by Country for Long-Lived Assets
Long-lived assets	26,083					25,359							26,083		25,359
Canada [Member]
Operating Revenues by Geographic Area
Operating revenues													7,039		6,115		6,841
Geographic Information by Country for Long-Lived Assets
Long-lived assets	1,915					1,816							1,915		1,816
U.K.and Ireland [Member]
Operating Revenues by Geographic Area
Operating revenues													11,556		10,797		11,232
Geographic Information by Country for Long-Lived Assets
Long-lived assets	$ 1,063					$ 967							1,063		967
Other Countries [Member]
Operating Revenues by Geographic Area
Operating revenues													$ 8,771		$ 7,268		$ 9,412

[1] During the quarter ended December 31, 2017, we recognized an income tax benefit of $1.9 billion related to Tax Reform as described in Note 14.

[2] During the quarter ended September 30, 2016, we recognized a tax benefit of $42 million related to the Aruba Disposition as described in Note 2.

[3] During the quarter ended June 30, 2016, we recognized a favorable noncash lower of cost or market inventory valuation adjustment of $454 million as described in Note 4 and an asset impairment loss of $56 million related to the Aruba Disposition as described in Note 2.

[4] During the quarter ended March 31, 2016, we recognized a favorable noncash lower of cost or market inventory valuation adjustment of $293 million as described in Note 4.

[5] Includes excise taxes on sales by certain of our international operations of $5,573 million, $5,493 million, and $5,980 million for the years ended December 31, 2017, 2016, and 2015.