revenue from contracts with customers - Revenues (Details) - Minimum - CAD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of transaction price allocated to remaining performance obligations
Transaction price allocated to remaining performance obligations	$ 3,008	$ 3,375
The 12-month period ending one year hence
Disclosure of transaction price allocated to remaining performance obligations
Transaction price allocated to remaining performance obligations	2,227	2,405
The 12-month period ending two years hence
Disclosure of transaction price allocated to remaining performance obligations
Transaction price allocated to remaining performance obligations	748	930
Thereafter
Disclosure of transaction price allocated to remaining performance obligations
Transaction price allocated to remaining performance obligations	$ 33	$ 40