Revenues and Accounts Receivable - Segment Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 5,963	$ 5,833	$ 3,225	$ 8,269	$ 9,154	$ 7,886	$ 8,253	$ 8,375	$ 23,290	$ 33,669	$ 34,055
Transportation
Disaggregation of Revenue [Line Items]
Total revenues									610	788	648
Facilities
Disaggregation of Revenue [Line Items]
Total revenues									622	609	588
Supply and Logistics
Disaggregation of Revenue [Line Items]
Total revenues									22,058	32,272	32,819
Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									25,455	35,371	35,812
Total revenues									25,217	35,767	35,973
Operating Segments | Transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									2,005	2,283	1,976
Total revenues									2,020	2,320	1,990
Operating Segments | Facilities
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									1,099	1,122	1,136
Total revenues									1,138	1,171	1,161
Operating Segments | Supply and Logistics
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers									22,351	31,966	32,700
Total revenues									22,059	32,276	32,822
Intersegment
Disaggregation of Revenue [Line Items]
Total revenues									(1,927)	(2,098)	(1,918)
Intersegment | Transportation
Disaggregation of Revenue [Line Items]
Total revenues									(1,004)	(1,061)	(874)
Intersegment | Facilities
Disaggregation of Revenue [Line Items]
Total revenues									(516)	(562)	(573)
Intersegment | Supply and Logistics
Disaggregation of Revenue [Line Items]
Total revenues									(1)	(4)	(3)
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenues									(238)	396	161
Other | Operating Segments | Transportation
Disaggregation of Revenue [Line Items]
Total revenues									15	37	14
Other | Operating Segments | Facilities
Disaggregation of Revenue [Line Items]
Total revenues									39	49	25
Other | Operating Segments | Supply and Logistics
Disaggregation of Revenue [Line Items]
Total revenues									$ (292)	$ 310	$ 122