Other Assets (Details) - CAD CAD in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Long-term materials	CAD 24	CAD 22
Prepaid leases	5	6
Unamortized fees on credit facility	5	7
Contracted customer incentives	11	2
Long-term receivables	1	2
Other	23	18
Total other assets	CAD 69	CAD 57