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Income Taxes (Effective Tax Rate) (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Income before provision for income taxes | $ 819 | $ 244
Statutory income tax rate | 31.00% | 31.00%
Income taxes, at statutory income tax rates | $ 254 | $ 76
Deferred income taxes on regulated income recorded as regulatory assets and regulatory liabilities | (54) | (47)
Financing deductions | (17) | (17)
Manufacturing And Investment Allowances | (8) | (7)
Foreign tax rate variance | 36 | (5)
Tax effect of equity earnings | (12) | (10)
Other | 4 | 1
Income Tax Expense (Benefit), Total | $ 520 | $ (22)
Effective Income Tax Rate Reconciliation, Percent | 63.00% | (9.00%)
Change in US Tax Reform [Abstract] |  |
Income Tax Reconciliation Revaluation Of US Non Regulated Deferred Income Taxes | $ 317 |
Statutory income tax rate | 31.00% | 31.00%
Deferred tax assets | $ 1,895 | $ 2,477
2018 tax rate [Member] |  |
Statutory income tax rate | 21.00% |
Change in US Tax Reform [Abstract] |  |
Income Tax Reconciliation Revaluation Of US Non Regulated Deferred Income Taxes | $ 1,100 |
Statutory income tax rate | 21.00% |
TECO Energy Inc [Member] |  |
Non-taxable portion of mark-to-market gains related to pending TECO Energy acquisition | $ 0 | (21)
Algonquin Power and Utilities Corporation [Member] |  |
Non-taxable portion of gains on transactions | $ 0 | $ 34

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