Revenues - Disaggregation of Revenue (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 2,292	$ 1,921	$ 6,291	$ 5,897
Leasing revenues	20	21	61	58
Total revenues	2,312	1,942	6,352	5,955
Freight
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,264	1,896	6,214	5,822
Total revenues	2,264	1,896	6,214	5,822
Grain
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	391	352	1,121	1,244
Coal
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	156	158	458	491
Potash
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	170	113	445	348
Fertilizers and sulphur
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	81	72	244	227
Forest products
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	109	89	299	259
Energy, chemicals and plastics
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	360	392	1,010	1,149
Metals, minerals and consumer products
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	246	196	655	535
Automotive
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	111	83	322	289
Intermodal
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	640	441	1,660	1,280
Non-freight excluding leasing revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 28	$ 25	$ 77	$ 75