INCOME TAXES - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 93	$ 82	$ 24	$ 26
Additions based on tax positions related to prior year	0	49	0
Additions based on tax positions related to the current year	11	9	0
Reductions for tax positions of prior years	0	0	(2)
Balance at end of year	$ 93	$ 82	$ 24	$ 26