EQUITY METHOD INTERESTS - Summary of Combined Statement of Operations Equity Method Interests (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Operating revenues	$ 4,308	$ 6,553	$ 7,764
Operating income (loss)	(4,102)	(2,152)	1,836
Net income (loss)	(4,904)	(3,682)	286
Other comprehensive loss	(2)	12	0
Equity Method Investment, Nonconsolidated Investee
Schedule of Equity Method Investments [Line Items]
Operating revenues	707	302	3
Operating income (loss)	331	121	(6)
Net income (loss)	256	120	(6)
Other comprehensive loss	$ 3	$ (8)	$ 0