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Significant Events - Million Dollar Financing (Details) - CAD ($) $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Jul. 20, 2018 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Aug. 02, 2018
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Bonds issued | $ 345 |  |  |  |
Borrowings, interest rate basis | .04509 |  |  |  |
Alberta Off-Coal Agreement | $ 40 | $ 40 | $ 40 | $ 0 |
Alberta off-coal agreement, annual cash payments, net | $ 37 |  |  |  |
Unsecured debentures |  |  |  |  |
Disclosure of detailed information about borrowings [line items] |  |  |  |  |
Interest rate | 6.40% |  |  |  | 6.40%

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