Other expense (income) (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Income and Expenses [Abstract]
Foreign exchange (gain) loss on debt and lease liabilities	$ (14)	$ (94)	$ 168
Other foreign exchange (gains) losses	(1)	(4)	3
Other	8	9	3
Other (income) expense	$ (7)	$ (89)	$ 174