PENSION AND OTHER POSTRETIREMENT BENEFITS - RETIREMENT SAVINGS PLAN (Details) - United States - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension and Other Postretirement Benefit Disclosures
Percent of match (percent)	6.00%
Total contributions by the Company	$ 27	$ 27	$ 27