Commitments and Contingencies - Narrative (Details) - CAD CAD in Millions		12 Months Ended
	Jul. 06, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Line Items]
Period for which future capital and operating expenditures are committed, beginning year		2016
Period for which future capital and operating expenditures are committed, end year		2032
Estimated future purchase commitment		CAD 800
Total minimum lease payments		553
Expenses for operating leases		127	CAD 121	CAD 154
Claimed loss or damages as a result of derailment [Member]
Commitments and Contingencies Disclosure [Line Items]
Amount of fund distribution		440
Lac-Megantic Rail Accident [Member]
Commitments and Contingencies Disclosure [Line Items]
Value of damages sought	CAD 409
Capital Expenditure [Member]
Commitments and Contingencies Disclosure [Line Items]
Total future committed expenditure		375
Operating Expenditures [Member]
Commitments and Contingencies Disclosure [Line Items]
Total future committed expenditure		CAD 1,500