Properties - Net Properties (Details) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Cost	CAD 23,225	CAD 20,943
Accumulated depreciation	6,952	6,505
Net book value	16,273	14,438
Depreciation expense	595	552	CAD 565
Software Development [Member]
Property, Plant and Equipment [Line Items]
Capitalized costs attributable to design and development	42	69	85
Depreciation expense	CAD 69	70	CAD 84
Track and railway [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	2.60%
Cost	CAD 16,303	14,515
Accumulated depreciation	4,427	4,126
Net book value	CAD 11,876	10,389
Buildings [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	3.20%
Cost	CAD 642	571
Accumulated depreciation	165	150
Net book value	CAD 477	421
Rolling stock [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	2.30%
Cost	CAD 4,041	3,737
Accumulated depreciation	1,524	1,414
Net book value	CAD 2,517	2,323
Information systems [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	12.20%
Cost	CAD 599	631
Accumulated depreciation	291	297
Net book value	CAD 308	334
Other [Member]
Property, Plant and Equipment [Line Items]
Average annual depreciation rate	3.50%
Cost	CAD 1,640	1,489
Accumulated depreciation	545	518
Net book value	CAD 1,095	CAD 971