Pension and Other Benefits - Narrative (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions made by the Company	$ 9	$ 17	$ 24	$ 40