Net Interest Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest Income (Expense), Net [Abstract]
Interest cost	$ 471	$ 475	$ 491
Interest capitalized to Properties	(17)	(20)	(16)
Interest expense	454	455	475
Interest income	(6)	(2)	(2)
Net interest expense	$ 448	$ 453	$ 473