share-based compensation - Employee share purchase plan (Details) - Employee share purchase plan - CAD ($) $ in Millions	3 Months Ended	6 Months Ended	9 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
share-based compensation
Dividend reinvestment in Common Shares	$ 9	$ 8	$ 18	$ 17
Purchase plan discount					0.00%

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