Accounts Receivable, Net - Schedule of Accounts Receivable (Details) - CAD ($) $ in Millions	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 1,092		$ 853
Allowance for credit losses	(39)	$ (39)	(34)	$ (38)	$ (38)	$ (40)
Total accounts receivable, net	1,053		819
Freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	835		614
Allowance for credit losses	(26)	(24)	(20)	(22)	(23)	(25)
Total accounts receivable, net	809		594
Non-freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	257		239
Allowance for credit losses	(13)	$ (15)	(14)	$ (16)	$ (15)	$ (15)
Total accounts receivable, net	$ 244		$ 225