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Income Taxes (Composition of taxes on income from continuing operations) (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |
Deferred income taxes | $ 381 | $ 125
Income tax expense (recovery) | 341 | 61
Supplemental Tax Information [Abstract] |  |
Income (loss) before provision for income taxes | 1,325 | 771
Canada |  |
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |
Current income taxes | 18 | (19)
Deferred income taxes | 20 | 45
Operating loss carry forwards | (46) | (48)
Supplemental Tax Information [Abstract] |  |
Income (loss) before provision for income taxes | 176 | 98
United States |  |
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |
Current income taxes | (58) | (46)
Deferred income taxes | 426 | 137
Investment tax credits | (10) | (9)
Supplemental Tax Information [Abstract] |  |
Income (loss) before provision for income taxes | 1,142 | 682
Other |  |
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |
Current income taxes | 0 | 1
Deferred income taxes | (9) | 0
Supplemental Tax Information [Abstract] |  |
Income (loss) before provision for income taxes | $ 7 | $ (9)

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