Operating Segments and Geographic Data - Segment Sales and Operating Revenues (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	$ 94,471	$ 139,865	$ 158,902
Oil and Gas
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	94,471	139,865	158,902
Oil and Gas \| Upstream
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	26,311	31,707	33,069
Oil and Gas \| Downstream
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	68,083	107,912	125,597
Oil and Gas \| Operating Segments
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	113,665	172,995	191,228
Oil and Gas \| Operating Segments \| United States
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	47,910	79,693	83,289
Oil and Gas \| Operating Segments \| International
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	65,755	93,302	107,939
Oil and Gas \| Operating Segments \| Upstream
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	41,381	58,986	60,713
Oil and Gas \| Operating Segments \| Upstream \| United States
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	14,577	23,358	22,891
Oil and Gas \| Operating Segments \| Upstream \| International
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	26,804	35,628	37,822
Oil and Gas \| Operating Segments \| Downstream
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	71,525	112,925	129,471
Oil and Gas \| Operating Segments \| Downstream \| United States
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	32,589	55,271	59,376
Oil and Gas \| Operating Segments \| Downstream \| International
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	38,936	57,654	70,095
Oil and Gas \| Intersegment \| United States
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	(667)	(818)	(786)
Oil and Gas \| Intersegment \| International
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	(15)	(20)	(22)
Oil and Gas \| Intersegment \| Upstream \| United States
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	(8,068)	(14,944)	(13,965)
Oil and Gas \| Intersegment \| Upstream \| International
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	(7,002)	(12,335)	(13,679)
Oil and Gas \| Intersegment \| Downstream \| United States
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	(2,150)	(3,924)	(2,742)
Oil and Gas \| Intersegment \| Downstream \| International
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	(1,292)	(1,089)	(1,132)
Oil and Gas \| Corporate And Eliminations [Member]
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	77	246	236
Oil and Gas \| Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	759	1,084	1,044
Oil and Gas \| Corporate, Non-Segment [Member] \| United States
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	744	1,064	1,022
Oil and Gas \| Corporate, Non-Segment [Member] \| International
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	15	20	22
Oil and Gas \| Intersegment Elimination \| United States
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	(10,885)	(19,686)	(17,493)
Oil and Gas \| Intersegment Elimination \| International
Segment Reporting Information [Line Items]
Total Sales and Other Operating Revenues	$ (8,309)	$ (13,444)	$ (14,833)