Properties - Net Properties (Details) - CAD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Cost	$ 67,489	$ 61,785
Accumulated depreciation	11,465	10,041
Net book value	$ 56,024	51,744
Track and roadway
Property, Plant and Equipment [Line Items]
Weighted-average annual depreciation rate	2.80%
Cost	$ 46,646	42,597
Accumulated depreciation	7,741	6,811
Net book value	$ 38,905	35,786
Rolling stock
Property, Plant and Equipment [Line Items]
Weighted-average annual depreciation rate	2.90%
Cost	$ 1,927	1,732
Accumulated depreciation	319	281
Net book value	1,608	1,451
Land
Property, Plant and Equipment [Line Items]
Cost	3,765	3,487
Accumulated depreciation	0	0
Net book value	$ 3,765	3,487
Buildings
Property, Plant and Equipment [Line Items]
Weighted-average annual depreciation rate	3.70%
Cost	$ 8,723	8,125
Accumulated depreciation	1,880	1,629
Net book value	$ 6,843	6,496
Concession land rights
Property, Plant and Equipment [Line Items]
Weighted-average annual depreciation rate	1.40%
Cost	$ 1,935	1,779
Accumulated depreciation	45	17
Net book value	$ 1,890	1,762
Other
Property, Plant and Equipment [Line Items]
Weighted-average annual depreciation rate	6.20%
Cost	$ 4,493	4,065
Accumulated depreciation	1,480	1,303
Net book value	3,013	2,762
Concessions
Property, Plant and Equipment [Line Items]
Cost	10,212	9,206
Accumulated depreciation	376	127
Net book value	9,836	9,079
Track and roadway
Property, Plant and Equipment [Line Items]
Cost	1,935	7,056
Accumulated depreciation	45	99
Net book value	1,890	6,957
Concession land rights
Property, Plant and Equipment [Line Items]
Cost	7,871	1,779
Accumulated depreciation	302	17
Net book value	7,569	1,762
Buildings
Property, Plant and Equipment [Line Items]
Cost	249	230
Accumulated depreciation	20	7
Net book value	229	223
Other
Property, Plant and Equipment [Line Items]
Cost	157	141
Accumulated depreciation	9	4
Net book value	$ 148	$ 137