STOCK OPTION AND STOCK UNIT PLANS - Narrative (Details) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024 CAD ($) compensationPlan shares	Dec. 31, 2023 CAD ($) shares	Dec. 31, 2022 CAD ($) shares
STOCK-BASED COMPENSATION
Number of long-term incentive compensation plans | compensationPlan	3
Compensation expense	$ 186	$ 154	$ 260
Common stock, shares authorized | shares	181	181	181
Incentive Stock Options
STOCK-BASED COMPENSATION
Compensation expense	$ 19	$ 18	$ 15
Vesting period (in years)	4 years
Expiration term (in years)	10 years
Unrecognized compensation cost related to non-vested share-based compensation arrangements granted	$ 12
Weighted average period over which compensation cost is expected to be recognized (in years)	2 years
Performance Stock Units (PSUs)
STOCK-BASED COMPENSATION
Compensation expense	$ 75	$ 59	$ 169
Vesting period (in years)	3 years
Weighted average period over which compensation cost is expected to be recognized (in years)	2 years
Period prior to the maturity of the grant for which weighted average share price is used to calculate cash awards (in days)	20 days
Performance multiplier	1.38	1.1	1.0
Unrecognized compensation expense related to non-vested units granted	$ 109
Performance Stock Units (PSUs) | Minimum
STOCK-BASED COMPENSATION
Performance multiplier	0
Performance Stock Units (PSUs) | Maximum
STOCK-BASED COMPENSATION
Performance multiplier	2.0
Restricted Stock Units (RSU)
STOCK-BASED COMPENSATION
Compensation expense	$ 92	$ 77	$ 76
Vesting period (in years)	3 years
Weighted average period over which compensation cost is expected to be recognized (in years)	1 year
Period prior to the maturity of the grant for which weighted average share price is used to calculate cash awards (in days)	20 days
Unrecognized compensation expense related to non-vested units granted	$ 67