EQUITY METHOD INTERESTS - Rollforward Activity (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	$ 1,555
Capital contributions	24	$ 154
Distributions	(76)
Equity income (loss), net	50
Accumulated other comprehensive income	1
Equity method interest, ending balance	1,554
Gulf Coast Express Pipeline, LLC
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	284
Capital contributions	0
Distributions	(25)
Equity income (loss), net	19
Accumulated other comprehensive income	0
Equity method interest, ending balance	278
EPIC Crude Holdings, LP
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	176
Capital contributions	1
Distributions	0
Equity income (loss), net	(11)
Accumulated other comprehensive income	1
Equity method interest, ending balance	167
Permian Highway Pipeline, LLC
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	615
Capital contributions	23
Distributions	(30)
Equity income (loss), net	27
Accumulated other comprehensive income	0
Equity method interest, ending balance	635
Shin Oak Pipeline (Breviloba, LLC)
Movement In Equity Method Interests [Roll Forward]
Equity method interest, beginning balance	480
Capital contributions	0
Distributions	(21)
Equity income (loss), net	15
Accumulated other comprehensive income	0
Equity method interest, ending balance	$ 474