Other (Income) Expense - Other Income and Expense (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Income and Expenses [Abstract]
Foreign exchange (gain) loss on debt and lease liabilities	$ (40)	$ 25	$ 89	$ (57)
Other foreign exchange losses (gains)	2	2	(2)	(4)
Other	2	2	2	3
Other (income) expense	$ (36)	$ 29	$ 89	$ (58)