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Income Taxes - Narrative (Details) - CAD ($) $ in Millions |  | 6 Months Ended | 12 Months Ended | 18 Months Ended | 24 Months Ended
--- | --- | --- | --- | --- | ---
Jan. 01, 2022 | Dec. 31, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Jun. 30, 2019 | Jan. 01, 2022
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |  |  |  |  |
Provincial corporate income tax rate | 8.00% | 11.00% |  | 12.00% | 11.00% |  |
Provincial corporate income tax rate, annual rate reduction |  |  |  |  |  |  | 1.00%
Increase in deferred income tax liability due to change in provincial corporate income tax rate |  |  | $ 1,618 | $ 10 |  |  |
Unused tax losses |  |  |  |  |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |  |  |  |  |
Deductible temporary differences for which no deferred tax asset is recognised |  | $ 1,000 | 1,000 |  |  |  |
Unused tax credits |  |  |  |  |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |  |  |  |  |
Deductible temporary differences for which no deferred tax asset is recognised |  | $ 750 | $ 750 |  |  |  |
Changes in tax rate |  |  |  |  |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |  |  |  |  |
Provincial corporate income tax rate |  |  |  |  |  | 12.00% |

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