Other (Income) Expense - Other Income and Expenses (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Income and Expenses [Abstract]
Foreign exchange loss (gain) on debt and lease liabilities	$ 25	$ (38)	$ (57)	$ 55
Other foreign exchange losses (gains)	2	(1)	(4)	2
Other	2	(8)	3	(1)
Other expense (income)	$ 29	$ (47)	$ (58)	$ 56