Other expense (income) (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Foreign exchange loss (gain) on long-term debt	$ 168	$ (186)	$ (79)
Other foreign exchange losses (gains)	3	(7)	(5)
Insurance recovery of legal settlement	0	(10)	0
Legal settlement	0	0	25
Charge on hedge roll and de-designation	0	13	0
Other	3	12	14
Total other expense (income)	$ 174	$ (178)	$ (45)