Other Long-Term Liabilities - Narrative (Details) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Liabilities Disclosure [Abstract]
Expected time period for payment of Provision for environmental remediation	10 years
Environmental remediation costs charged to income	CAD 5	CAD 6	CAD 7