share-based compensation - Employee share purchase plan (Details) - Employee share purchase plan - CAD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2019 |
Jun. 30, 2018 |
Jun. 30, 2019 |
Jun. 30, 2018 |
|
| share-based compensation | ||||
| Dividend reinvestment in Common Shares | $ 8 | $ 9 | $ 17 | $ 17 |
| Purchase plan discount | 0.00% | 0.00% | ||