Accounts Receivable, Net - Allowance for Credit Loss (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, opening balance	$ (39)	$ (38)	$ (34)	$ (40)
Current period credit loss provision, net	0	0	(5)	2
Allowance for credit losses, closing balance	(39)	(38)	(39)	(38)
Freight
Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, opening balance	(24)	(23)	(20)	(25)
Current period credit loss provision, net	(2)	1	(6)	3
Allowance for credit losses, closing balance	(26)	(22)	(26)	(22)
Non-freight
Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, opening balance	(15)	(15)	(14)	(15)
Current period credit loss provision, net	2	(1)	1	(1)
Allowance for credit losses, closing balance	$ (13)	$ (16)	$ (13)	$ (16)