Other expense (income) (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Income and Expenses [Abstract]
Foreign exchange (gain) loss on debt and lease liabilities	$ (94)	$ 168	$ (186)
Other foreign exchange (gains) losses	(4)	3	(7)
Insurance recovery of legal settlement	0	0	(10)
Charge on hedge roll and de-designation	0	0	13
Other	9	3	12
Other (income) expense	$ (89)	$ 174	$ (178)