Revenues - Contract Liabilities (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Contract with Customer, Liability [Abstract]
Opening balance, January 1	$ 64	$ 67
Contract liabilities assumed upon the acquisition of KCS (Note 11)	7	0
Revenue recognized in the period that was included in the opening balance or liabilities assumed	36	21
Increase due to consideration received, net of revenue recognized in the period	17	18
Closing balance, December 31	$ 52	$ 64