Revenues (Details) - CAD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									$ 7,729	$ 7,254	$ 6,492
Leasing revenues									63	62	62
Total revenues	$ 2,069	$ 1,979	$ 1,977	$ 1,767	$ 2,006	$ 1,898	$ 1,750	$ 1,662	7,792	7,316	6,554
Grain
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									1,684	1,566	1,532
Coal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									682	673	631
Potash
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									462	486	411
Fertilizers and sulphur
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									250	243	241
Forest products
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									304	284	265
Energy, chemicals, and plastics
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									1,534	1,243	898
Metals, minerals, and consumer products
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									752	797	739
Automotive
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									352	322	293
Intermodal
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									1,593	1,538	1,365
Freight
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									7,613	7,152	6,375
Non-freight excluding leasing revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									$ 116	$ 102	$ 117