Changes in Accumulated Other Comprehensive Loss ("AOCL") by Component - Amounts in Pension and Post-retirement Defined Benefit Plans Reclassified from AOCL (Details) - Reclassification out of Accumulated Other Comprehensive Income - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Recognition of net actuarial loss	$ 38	$ 52	$ 77	$ 105
Income tax recovery	(10)	(13)	(18)	(27)
Total net of income tax	$ 28	$ 39	$ 59	$ 78