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Commitments and Contingencies (Guarantees and Letters of Credit) (Details) $ in Millions, $ in Millions | Dec. 31, 2019 CAD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 CAD ($) | Dec. 31, 2018 USD ($)
--- | --- | --- | --- | ---
Guarantor Obligations [Line Items] |  |  |  |
Letters of Credit Outstanding, Amount | $ 3 |  | $ 3 |
Nova Scotia Power Inc. [Member] |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |
Letters of Credit Outstanding, Amount |  | $ 52 |  | $ 49
Payment Guarantee | SeaCoast Gas Transmission, LLC |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |
Guaranty Liabilities |  | 45 |  |
Letters of Credit Outstanding, Amount |  | 27 |  |
Surety Bonds |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |
Letters of Credit Outstanding, Amount |  | $ 82 |  | $ 67

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