PENSION AND OTHER POSTRETIREMENT BENEFITS - Actuarial Assumptions (Details)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Canada | Pension
Projected benefit obligation
Discount rate	4.70%	4.60%	5.10%
Rate of salary increase	3.00%	3.00%	2.90%
Net periodic benefit cost
Discount rate	4.60%	5.30%	3.20%
Rate of return on plan assets	6.80%	6.50%	6.60%
Rate of salary increase	3.00%	2.90%	2.90%
Canada | OPEB
Projected benefit obligation
Discount rate	4.70%	4.60%	5.30%
Net periodic benefit cost
Discount rate	4.60%	5.30%	3.20%
US | Pension
Projected benefit obligation
Discount rate	5.50%	4.70%	4.90%
Rate of salary increase	2.60%	2.60%	2.80%
Cash balance interest credit rate	4.00%	4.50%	4.30%
Net periodic benefit cost
Discount rate	4.80%	4.90%	2.60%
Rate of return on plan assets	7.30%	7.40%	7.40%
Rate of salary increase	2.80%	2.80%	2.80%
Cash balance interest credit rate	4.40%	4.30%	4.30%
US | OPEB
Projected benefit obligation
Discount rate	5.30%	4.70%	4.90%
Net periodic benefit cost
Discount rate	5.50%	4.90%	2.40%
Rate of return on plan assets	6.70%	5.90%	6.00%