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Income Taxes (Deferred) (Details) - CAD CAD in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Components of Deferred Tax Assets [Abstract] |  |
Deferred Tax Assets, Tax Loss Carry Forwards | CAD 1,036 | CAD 72
Tax credit carry forwards | 318 | 7
Regulatory liabilities - cost of removal | 388 | 42
Deferred Tax Assets, Derivative Instruments | 173 | 204
Pension and post-retirement liabilities | 147 | 129
Regulatory liabilities | 101 | 94
Asset retirement obligations | 47 | 47
Deferred Tax Assets, Goodwill and Intangible Assets | 0 | 0
Deferred Tax Assets, Other | 355 | 136
Deferred Tax Assets, Gross, Total | 2,565 | 731
Deferred Tax Assets, Valuation Allowance | (58) | (18)
Deferred Tax Assets, Net of Valuation Allowance, Total | 2,507 | 713
Components of Deferred Tax Liabilities [Abstract] |  |
Deferred Tax Liabilities, Property, Plant and Equipment | (3,625) | (960)
Deferred Tax Liabilities, Derivatives | (202) | (264)
Deferred Tax Liabilities, Leasing Arrangements | (103) | (89)
Deferred Tax Liabilities, Other | (124) | (130)
Deferred Tax Liabilities, Gross, Total | (4,054) | (1,443)
Noncurrent Deferred Tax Liabilities And Assets [Abstract] |  |
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent | 125 | 32
Deferred Tax Liabilities, Net, Noncurrent | (1,672) | (762)
Deferred Tax Assets (Liabilities), Net, Noncurrent, Total | CAD (1,547) | CAD (730)

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