Revenues - Disaggregation of Revenue (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 2,181	$ 2,034	$ 3,999	$ 3,976
Leasing revenues	21	20	41	37
Total revenues	2,202	2,054	4,040	4,013
Freight
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,154	2,008	3,950	3,926
Total revenues	2,154	2,008	3,950	3,926
Grain
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	370	444	730	892
Coal
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	163	170	302	333
Potash
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	171	134	275	235
Fertilizers and sulphur
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	85	78	163	155
Forest products
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	104	90	190	170
Energy, chemicals and plastics
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	340	369	650	757
Metals, minerals and consumer products
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	228	180	409	339
Automotive
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	120	98	211	206
Intermodal
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	573	445	1,020	839
Non-freight excluding leasing revenues
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 27	$ 26	$ 49	$ 50