STOCK OPTION AND STOCK UNIT PLANS - STOCK OPTION ACTIVITY (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2021 CAD ($) compensationPlan $ / shares shares	Dec. 31, 2020 CAD ($) $ / shares shares	Dec. 31, 2019 CAD ($)
STOCK OPTION AND STOCK UNIT PLANS
Number of long-term incentive compensation plans | compensationPlan	3
Compensation expense	$ 157	$ 145	$ 117
INCENTIVE STOCK OPTIONS
STOCK OPTION AND STOCK UNIT PLANS
Compensation expense	$ 16	$ 24	32
Vesting period	4 years
Expiration term	10 years
Number
Options outstanding at beginning of year (in shares) | shares	35,494
Options granted (in shares) | shares	4,072
Options exercised (in shares) | shares	(4,142)
Options cancelled or expired (in shares) | shares	(1,407)
Options outstanding at end of year (in shares) | shares	34,017	35,494
Options vested at end of year (in shares) | shares	22,029
Weighted Average Exercise Price
Options outstanding at beginning of year (in dollars per share) | $ / shares	$ 48.65
Options granted (in dollars per share) | $ / shares	43.86
Options exercised (in dollars per share) | $ / shares	41.85
Options cancelled or expired (in dollars per share) | $ / shares	50.74
Options outstanding at end of year (in dollars per share) | $ / shares	49.28	$ 48.65
Options vested at end of year (in dollars per share) | $ / shares	$ 49.84
Weighted Average Remaining Contractual Life (years)
Options outstanding at end of year	5 years 8 months 12 days
Options vested at end of year	4 years 6 months
Aggregate Intrinsic Value
Options outstanding at end of year	$ 128
Options vested at end of year	64
Stock options, additional disclosures
Total intrinsic value of awards exercised	24	$ 13	58
Cash received on exercise of awards	2	4	1
Total fair value of options vested	$ 25	$ 30	$ 32