Net Interest Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Income (Expense), Net [Abstract]
Interest cost	$ 475	$ 491	$ 497
Interest capitalized to Properties	(20)	(16)	(25)
Interest expense	455	475	472
Interest income	(2)	(2)	(1)
Net interest expense	$ 453	$ 473	$ 471