Accounts receivable, net - Schedule of Accounts Receivable (Details) - CAD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 853	$ 865
Allowance for credit losses	(34)	(40)	$ (43)
Total accounts receivable, net	819	825
Freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	614	662
Allowance for credit losses	(20)	(25)	(27)
Total accounts receivable, net	594	637
Non-freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	239	203
Allowance for credit losses	(14)	(15)	$ (16)
Total accounts receivable, net	$ 225	$ 188