EQUITY METHOD INTERESTS - Summary of Investments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity method interests	$ 1,567	$ 1,555
Gulf Coast Express Pipeline, LLC
Schedule of Equity Method Investments [Line Items]
Interest percentage	16.00%
Equity method interests	$ 281	284
EPIC Crude Holdings, LP
Schedule of Equity Method Investments [Line Items]
Interest percentage	15.00%
Equity method interests	$ 172	176
Permian Highway Pipeline, LLC
Schedule of Equity Method Investments [Line Items]
Interest percentage	26.70%
Equity method interests	$ 639	615
Shin Oak Pipeline (Breviloba, LLC)
Schedule of Equity Method Investments [Line Items]
Interest percentage	33.00%
Equity method interests	$ 475	$ 480