Other (Income) Expense (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Foreign exchange (gain) loss on long-term debt	$ (38)	$ (105)	$ 55	$ (200)
Other foreign exchange (gains) losses	(1)	(3)	2	(5)
Insurance recovery of legal settlement	0	0	0	(10)
Charge on hedge roll and de-designation	0	0	0	13
Other	(8)	3	(1)	8
Total other (income) expense	$ (47)	$ (105)	$ 56	$ (194)