Accounts Receivable, Net - Schedule of Accounts Receivable (Details) - CAD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	$ 816
Allowance for credit losses	(40)	$ (41)	$ (43)
Total accounts receivable, net	776
Freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	633
Allowance for credit losses	(26)	(27)	(27)
Total accounts receivable, net	607
Non-freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total accounts receivable	183
Allowance for credit losses	(14)	$ (14)	$ (16)
Total accounts receivable, net	$ 169