STOCK-BASED COMPENSATION - Expense for performance based shares units (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share plan expense	$ 10	$ 12	$ 27
Performance share plan, shares issued in period	505	315	249
Total Stockholder Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share plan expense	$ 5	$ 5	$ 9
Performance share plan, shares issued in period	165	0	0
Relative Revenue Growth
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share plan expense	$ 4	$ 7	$ 18
Performance share plan, shares issued in period	340	315	249
Adjusted Earnings Per Share
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share plan expense	$ 1	$ 0	$ 0
Performance share plan, shares issued in period	0	0	0