Other comprehensive income (loss) and accumulated other comprehensive loss - Amounts in Pension and Post-Retirement Defined Benefit Plans Reclassification from AOCL (Details) - Reclassification out of Accumulated Other Comprehensive Loss - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of prior service costs	$ 0	$ (1)
Recognition of net actuarial loss	210	180
Total before income tax	210	179
Income tax recovery	(55)	(47)
Total net of income tax	$ 155	$ 132