Property Sale (Details) - Chicago property and easements - CAD ($) $ in Millions	3 Months Ended
	Jun. 30, 2021	Mar. 31, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from exchanged property and construction easements		$ 103
Cash proceeds from properties and easements		61
Property assets, Fair value acquired		42
Gain on exchange of properties and easements	$ 4	50
Gain on exchange of property and easements, after tax		38
Deferred gain on exchange of property and easements		$ 53