Revenues - Contract Liabilities (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Contract with Customer, Liability [Abstract]
Opening balance, January 1	$ 52	$ 64
Contract liabilities assumed upon the acquisition of KCS (Note 10)	0	7
Revenue recognized in the period that was included in the opening balance or liabilities assumed	(33)	(36)
Increase due to consideration received, net of revenue recognized in the period	16	17
Closing balance, December 31	$ 35	$ 52