EQUITY METHOD INTERESTS - Summary of Investments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity method interests	$ 1,555	$ 1,258
Shin Oak Pipeline (Breviloba, LLC)
Schedule of Equity Method Investments [Line Items]
Equity method interests		493
ALTM
Schedule of Equity Method Investments [Line Items]
Equity method interests	$ 1,555	1,258	$ 91
ALTM | Gulf Coast Express Pipeline LLC
Schedule of Equity Method Investments [Line Items]
Interest	16.00%
Equity method interests	$ 284	291	91
ALTM | EPIC Crude Holdings, LP
Schedule of Equity Method Investments [Line Items]
Interest	15.00%
Equity method interests	$ 176	163	0
ALTM | Permian Highway Pipeline LLC
Schedule of Equity Method Investments [Line Items]
Interest	26.70%
Equity method interests	$ 615	311	0
ALTM | Shin Oak Pipeline (Breviloba, LLC)
Schedule of Equity Method Investments [Line Items]
Interest	33.00%
Equity method interests	$ 480	$ 493	$ 0