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INVESTMENTS - Summary of Investments (Details) - CAD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of detailed information about financial instruments [line items] |  |
Investments | $ 893 | $ 913
Investment in PrairieSky Royalty Ltd. |  |
Disclosure of detailed information about financial instruments [line items] |  |
Investments | 726 | 723
Investment in Inter Pipeline Ltd. |  |
Disclosure of detailed information about financial instruments [line items] |  |
Investments | $ 167 | $ 190

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- Details
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