EMPLOYEE BENEFIT PLANS - Discount rate and assumptions (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Supplemental Benefit Plan
Weighted-average assumptions used to determine nonunion benefit obligations
Discount rate (as a percent)	4.30%	4.60%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	4.60%	1.80%	1.10%
Postretirement Health Benefit Plan
Weighted-average assumptions used to determine nonunion benefit obligations
Discount rate (as a percent)	4.80%	5.00%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	5.00%	2.70%	2.30%