Pension and Other Benefits - Net Periodic Benefit Cost for DB Pension Plans and Other Benefits (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Defined Benefit Plan and Other Postretirement Benefit Plans
Total other components of net periodic benefit (recovery) cost	$ (101)	$ (96)	$ (202)	$ (191)
Defined Benefit Pension Plan
Defined Benefit Plan and Other Postretirement Benefit Plans
Current service cost (benefits earned by employees)	37	43	74	86
Interest cost on benefit obligation	96	88	192	176
Expected return on fund assets	(239)	(240)	(479)	(480)
Recognized net actuarial loss	38	51	76	103
Total other components of net periodic benefit (recovery) cost	(105)	(101)	(211)	(201)
Net periodic benefit (recovery) cost	(68)	(58)	(137)	(115)
Other Post-retirement Benefit Plans
Defined Benefit Plan and Other Postretirement Benefit Plans
Current service cost (benefits earned by employees)	3	3	5	6
Interest cost on benefit obligation	4	4	8	8
Expected return on fund assets	0	0	0	0
Recognized net actuarial loss	0	1	1	2
Total other components of net periodic benefit (recovery) cost	4	5	9	10
Net periodic benefit (recovery) cost	$ 7	$ 8	$ 14	$ 16