EQUITY METHOD INTERESTS - Summary of Combined Statement of Operations Equity Method Interests (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of Equity Method Investments [Line Items]
Operating income	$ 822	$ 206	$ 2,090	$ (4,287)
Net income	$ 0	$ 41	890	(4,959)
Equity Method Investment, Nonconsolidated Investee or Group of Investees
Schedule of Equity Method Investments [Line Items]
Operating revenues			812	531
Operating income			401	267
Net income			340	217
Other comprehensive income (loss)			$ 4	$ (1)