STOCK OPTION AND STOCK UNIT PLANS - Stock Option Activity (Details) - Incentive Stock Options - CAD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Number
Options outstanding at beginning of year (in shares)	27,624
Options granted (in shares)	3,053
Options exercised (in shares)	(648)
Options cancelled or expired (in shares)	(1,300)
Options outstanding at end of year (in shares)	28,729	27,624
Options vested at end of year (in shares)	20,235
Weighted Average Exercise Price
Options outstanding at beginning of year (in Canadian dollars per share)	$ 48.46
Options granted (in Canadian dollars per share)	53.11
Options exercised (in Canadian dollars per share)	45.70
Options cancelled or expired (in Canadian dollars per share)	53.84
Options outstanding at end of year (in Canadian dollars per share)	50.79	$ 48.46
Options vested at end of year (in Canadian dollars per share)	$ 50.64
Weighted Average Remaining Contractual Life (years)
Options outstanding at end of year	5 years 3 months 18 days
Options vested at end of year	4 years 1 month 6 days
Aggregate Intrinsic Value
Options outstanding at end of year	$ 45
Options vested at end of year	36
Stock options, additional disclosures
Total intrinsic value of awards exercised	2	$ 66	$ 24
Cash received on exercise of awards		3	2
Total fair value of options vested	$ 20	$ 21	$ 25