Net Interest Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest Income (Expense), Net [Abstract]
Interest cost	$ 478	$ 471	$ 475
Interest capitalized to Properties	(16)	(17)	(20)
Interest expense	462	454	455
Interest income	(4)	(6)	(2)
Net interest expense	$ 458	$ 448	$ 453