Accounts Receivable, Net (Details) - CAD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross	$ 847	$ 845
Allowance for doubtful accounts	(42)	(30)
Accounts receivable, net	805	815
Freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross	637	677
Non-freight
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, gross	$ 210	$ 168