Pension and Other Benefits - Narrative (Details) - Pension Plans, Defined Benefit [Member] - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Contributions made by the company	$ 17	$ 13	$ 40	$ 25
Refund of plan surplus				$ 10