Other Income and Charges (Details) - CAD CAD in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Income and Expenses [Abstract]
Foreign exchange (gains) losses on long-term debt	CAD (105)	CAD 46	CAD (200)	CAD (153)
Other foreign exchange (gains) losses	(3)	2	(5)	(5)
Legal settlement	0	25	0	25
Insurance recovery of legal settlement	0	0	(10)	0
Charge on hedge roll and de-designation	0	0	13	0
Other	3	(2)	8	14
Total other income and charges	CAD (105)	CAD 71	CAD (194)	CAD (119)