Accounts Receivable, Net - Schedule of Accounts Receivable (Details) - CAD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 854	$ 853
Allowance for credit losses	(36)	(34)	$ (39)	$ (40)
Total accounts receivable, net	818	819
Freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	599	614
Allowance for credit losses	(22)	(20)	(24)	(25)
Total accounts receivable, net	577	594
Non-freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	255	239
Allowance for credit losses	(14)	(14)	$ (15)	$ (15)
Total accounts receivable, net	$ 241	$ 225