INCOME TAXES - Summary of Valuation Allowance Against Certain Foreign Net Deferred Tax Assets and State Net Operating Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Movement in Valuation Allowance of Deferred Tax Assets [Roll Forward]
Balance at beginning of year	$ 4,959	$ 3,947	$ 3,816
State	67	41	15
U.S.	960	971	124
Foreign	5	0	(8)
Balance at end of year	$ 5,991	$ 4,959	$ 3,947