Properties - Net Properties (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Cost	$ 26,382	$ 24,429
Accumulated depreciation	7,964	7,413
Net book value	18,418	17,016
Depreciation expense	$ 696	661	$ 640
Track and railway [Member]
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	2.80%
Cost	$ 18,599	17,285
Accumulated depreciation	5,236	4,814
Net book value	$ 13,363	12,471
Buildings [Member]
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	3.00%
Cost	$ 781	719
Accumulated depreciation	218	196
Net book value	$ 563	523
Rolling stock [Member]
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	2.80%
Cost	$ 4,467	4,114
Accumulated depreciation	1,613	1,557
Net book value	$ 2,854	2,557
Information systems [Member]
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	10.40%
Cost	$ 551	551
Accumulated depreciation	252	264
Net book value	$ 299	287
Other [Member]
Property, Plant and Equipment [Line Items]
Weighted average annual depreciation rate	5.10%
Cost	$ 1,984	1,760
Accumulated depreciation	645	582
Net book value	1,339	1,178
Internal-use Software Development [Member]
Property, Plant and Equipment [Line Items]
Capitalized costs attributable to design and development	53	49	46
Depreciation expense	$ 49	$ 55	$ 63