Accounts Receivable, Net - Allowance for Credit Loss (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, opening balance	$ (36)	$ (39)	$ (34)	$ (40)
Current period credit loss provision, net	(3)	1	(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	(22)	(24)	(20)	(25)
Current period credit loss provision, net	(2)	1	(4)	2
Allowance for credit losses, closing balance	(24)	(23)	(24)	(23)
Non-freight
Allowance for Credit Loss [Roll Forward]
Allowance for credit losses, opening balance	(14)	(15)	(14)	(15)
Current period credit loss provision, net	(1)	0	(1)	0
Allowance for credit losses, closing balance	$ (15)	$ (15)	$ (15)	$ (15)