Accounts Receivable, Net - Schedule of Accounts Receivable (Details) - CAD ($) $ in Millions	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 1,001		$ 853
Allowance for credit losses	(39)	$ (36)	(34)	$ (38)	$ (39)	$ (40)
Total accounts receivable, net	962		819
Freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	736		614
Allowance for credit losses	(24)	(22)	(20)	(23)	(24)	(25)
Total accounts receivable, net	712		594
Non-freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	265		239
Allowance for credit losses	(15)	$ (14)	(14)	$ (15)	$ (15)	$ (15)
Total accounts receivable, net	$ 250		$ 225