Business acquisition - Pro Forma Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 CAD ($)	Mar. 31, 2023 CAD ($)
Business Acquisition [Line Items]
KCS historical, revenue	$ 0	$ 1,187
Pro forma CPKC, revenue	3,520	3,456
KCS historical, net income attributable to controlling shareholders	0	246
Pro forma, net income attributable to controlling shareholders	775	756
Total operating expenses	2,371	1,437
Operating income	1,149	829
Other (income) expense (Note 8)	(2)	2
Income before income taxes	$ 1,033	$ 963
Daily exchange rate used, revenue		1.35
KCS
Business Acquisition [Line Items]
Total operating expenses		$ 779
Operating income		408
Income before income taxes		$ 334