Properties - Net Properties (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Cost	$ 29,851	$ 29,051
Accumulated depreciation	8,651	8,629
Net book value	21,200	20,422
Capitalized internal-use software, Costs	47	45	$ 55
Capitalized internal-use software, Depreciation	$ 40	42	$ 44
Track and roadway
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	2.80%
Cost	$ 21,210	20,676
Accumulated depreciation	5,893	5,859
Net book value	$ 15,317	14,817
Buildings
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	2.90%
Cost	$ 1,022	937
Accumulated depreciation	266	259
Net book value	$ 756	678
Rolling stock
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	2.90%
Cost	$ 4,793	4,702
Accumulated depreciation	1,419	1,498
Net book value	$ 3,374	3,204
Information systems software
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	8.10%
Cost	$ 603	569
Accumulated depreciation	279	253
Net book value	$ 324	316
Other
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	5.30%
Cost	$ 2,223	2,167
Accumulated depreciation	794	760
Net book value	$ 1,429	$ 1,407