Other Assets (Details) - CAD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Operating lease ROU assets	$ 316	$ 358
Contracted customer incentives	60	32
Long-term materials	37	41
Other	25	20
Total other assets	$ 438	$ 451