PENSION AND OTHER POSTRETIREMENT BENEFITS - Retirement Savings Plan (Details) - US - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension and Other Postretirement Benefit Disclosures
Percent of match (percent)	6.00%
Total contributions by the Company	$ 33	$ 30	$ 27