Properties - Net Properties (Details) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Cost	CAD 23,814	CAD 23,225
Accumulated depreciation	7,125	6,952
Net book value	16,689	16,273
Depreciation expense	CAD 640	595	CAD 552
Track and railway [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	2.80%
Cost	CAD 16,817	16,303
Accumulated depreciation	4,573	4,427
Net book value	CAD 12,244	11,876
Buildings [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	3.00%
Cost	CAD 662	642
Accumulated depreciation	178	165
Net book value	CAD 484	477
Rolling stock [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	2.80%
Cost	CAD 4,060	4,041
Accumulated depreciation	1,524	1,524
Net book value	CAD 2,536	2,517
Information systems [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	11.70%
Cost	CAD 584	599
Accumulated depreciation	299	291
Net book value	CAD 285	308
Other [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	5.30%
Cost	CAD 1,691	1,640
Accumulated depreciation	551	545
Net book value	1,140	1,095
Software Development [Member]
Property, Plant and Equipment [Line Items]
Capitalized costs attributable to design and development	46	42	69
Depreciation expense	CAD 63	CAD 69	CAD 70