Other (Income) Expense - Other Income and Expense (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Income and Expenses [Abstract]
Foreign exchange (gain) loss on debt and lease liabilities	$ (33)	$ 215
Other foreign exchange losses (gains)	1	(5)
Acquisition-related costs, Other (income) expense	3	0
Other	1	1
Other (income) expense	$ (28)	$ 211