EQUITY METHOD INTERESTS - Rollforward Activity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	$ 1,555
Capital contributions	21	$ 83
Distributions	(31)
Equity income (loss), net	21
Accumulated other comprehensive income	1
Equity method interest, ending balance	1,567
Gulf Coast Express Pipeline, LLC
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	284
Capital contributions	0
Distributions	(12)
Equity income (loss), net	9
Accumulated other comprehensive income	0
Equity method interest, ending balance	281
EPIC Crude Holdings, LP
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	176
Capital contributions	0
Distributions	0
Equity income (loss), net	(5)
Accumulated other comprehensive income	1
Equity method interest, ending balance	172
Permian Highway Pipeline, LLC
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	615
Capital contributions	21
Distributions	(8)
Equity income (loss), net	11
Accumulated other comprehensive income	0
Equity method interest, ending balance	639
Undistributed earnings	3
Shin Oak Pipeline (Breviloba, LLC)
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	480
Capital contributions	0
Distributions	(11)
Equity income (loss), net	6
Accumulated other comprehensive income	0
Equity method interest, ending balance	$ 475