Revenues - Disaggregation of Revenue (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1,818	$ 1,942
Leasing revenues	20	17
Total revenues	1,838	1,959
Freight
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,796	1,918
Total revenues	1,796	1,918
Grain
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	360	448
Coal
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	139	163
Potash
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	104	101
Fertilizers and sulphur
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	78	77
Forest products
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	86	80
Energy, chemicals and plastics
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	310	388
Metals, minerals and consumer products
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	181	159
Automotive
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	91	108
Intermodal
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	447	394
Non-freight excluding leasing revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 22	$ 24