EQUITY METHOD INTERESTS - Summary of Combined Statement of Operations Equity Method Interests (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Equity Method Investments [Line Items]
Operating revenues	$ 1,144	$ 1,500	$ 3,019	$ 4,775
Operating expenses	914	1,286	7,503	4,043
Operating income	206	182	(4,287)	719
Net income	41	(117)	$ (4,959)	$ (435)
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Operating revenues	531	103
Operating expenses	264	62
Operating income	267	41
Net income	217	34
Other comprehensive loss	$ (1)	$ (11)