Other Long-Term Liabilities (Details) - CAD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Other Liabilities Disclosure [Abstract]
Stock-based compensation liabilities, net of current portion	$ 146	$ 111
Provision for environmental remediation, net of current portion	71	70
Deferred revenue, net of current portion	34	4
Deferred real estate lease and license revenue, net of current portion	18	20
Deferred gains on sale leaseback transactions	5	6
Other, net of current portion	63	66
Other long-term liabilities	585	562
Aggregate provision for environmental remediation, including current portion	$ 80	$ 77