PENSION AND OTHER POSTRETIREMENT BENEFITS (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 45	$ 48
Interest cost	41	32
Expected return on plan assets1	(98)	(84)
Amortization of actuarial (gain)/loss1	(1)	14
Net periodic benefit (credit)/cost	$ (13)	$ 10