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Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions | Dec. 31, 2019 CAD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 CAD ($)
--- | --- | --- | ---
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] |  |  |
Short-term Investments | $ 0 |  | $ 43,000,000
Investment Interest Rate |  |  | 2.00%
Asset Impairment Charges |  |  |
Regulatory Assets | 1,552,000,000 |  | $ 1,569,000,000
Net book value | $ 16,576,000,000 |  | $ 17,476,000,000
Asset Impairment for Regulatory Action [Member] | Hurricane Dorian [Member] | GBPC |  |  |
Asset Impairment Charges |  |  |
Regulatory Assets |  | $ 3 |
Offsetting insurance receivable |  | 15 |
Net book value |  | $ 18 |

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