Other Income and Charges (Details) - CAD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Income and Expenses [Abstract]
Foreign exchange loss (gain) on long-term debt	$ 49	$ (28)
Other foreign exchange gains	(1)	(1)
Other	3	1
Total other income and charges	$ 51	$ (28)