INCOME TAXES - Unrecognized Tax Benefit Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning of the period	$ 11	$ 7	$ 7
Additions related to prior year tax positions	5	4	0
Additions related to current year tax positions	3	0	2
Reductions related to prior year tax positions	(1)	0	(1)
Reductions related to settlements with taxing authorities	(4)	0	0
Reductions related to expiration of the applicable statute of limitations	(3)	0	(1)
Balance at the end of the period	$ 11	$ 11	$ 7