Revenues - Contract Liabilities (Details) - CAD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Contract with Customer, Liability [Abstract]
Opening balance	$ 79	$ 74	$ 146	$ 2
Revenue recognized that was included in the contract liability balance at the beginning of the period	(25)	(8)	(95)	(2)
Increase due to consideration received, net of revenue recognized during the period	5	4	8	70
Closing balance	$ 59	$ 70	$ 59	$ 70