Revenues - Contract Liabilities (Details) - CAD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Contract with Customer, Liability [Abstract]
Opening balance	$ 114	$ 112	$ 61	$ 146
Revenue recognized that was included in the contract liability balance at the beginning of the period	(19)	(37)	(23)	(73)
Increase due to consideration received, net of revenue recognized during the period	150	4	207	6
Closing balance	$ 245	$ 79	$ 245	$ 79