Other (Income) Expense - Other Income and Expense (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Other Income and Expenses [Abstract]
Foreign exchange loss (gain) on debt and lease liabilities	$ 215	$ (45)
Other foreign exchange gains	(5)	(3)
Other	1	1
Other expense (income)	$ 211	$ (47)