SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue recognized	$ 246
Largest Non-Affiliated Customer | Sales Revenue, Net | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration (percent)	10.00%	10.00%	13.50%
Transportation revenue
Disaggregation of Revenue [Line Items]
Revenue recognized	$ 210	$ 238	$ 127