Other Assets (Details) - CAD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Operating leases	$ 358		$ 0
Long-term materials	41		26
Contracted customer incentives	32		11
Prepaid leases	0		10
Other	20		24
Total other assets	$ 451	$ 470	$ 71