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Investments - Inter Pipeline (Details) - CAD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of financial assets [line items] |  |  |
(Gain) loss from investment | $ 293 | $ 346 | $ (38)
Investment in Inter Pipeline Ltd. |  |  |
Disclosure of financial assets [line items] |  |  |
Fair value (gain) loss from Inter Pipeline | (21) | 43 | 23
Dividend income from Inter Pipeline | (11) | (11) | (10)
(Gain) loss from investment | $ (32) | $ 32 | $ 13

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