Properties - Net Properties (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Property, Plant and Equipment [Line Items]
Cost	$ 27,255	$ 26,382
Accumulated depreciation	8,099	7,964
Net book value	19,156	18,418		$ 18,406
Capitalized internal-use software costs	55	53	$ 49
Capitalized internal-use software, Depreciation	$ 44	49	$ 55
Track and roadway
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	2.80%
Cost	$ 19,299	18,599
Accumulated depreciation	5,522	5,236
Net book value	$ 13,777	13,363
Buildings
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	2.90%
Cost	$ 833	781
Accumulated depreciation	237	218
Net book value	$ 596	563
Rolling stock
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	2.80%
Cost	$ 4,529	4,467
Accumulated depreciation	1,445	1,613
Net book value	$ 3,084	2,854
Information systems software
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	10.00%
Cost	$ 527	551
Accumulated depreciation	215	252
Net book value	$ 312	299
Other
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	5.20%
Cost	$ 2,067	1,984
Accumulated depreciation	680	645
Net book value	$ 1,387	$ 1,339