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OTHER LONG-TERM LIABILITIES - Segmented Asset Retirement Obligations (Details) - CAD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | --- | --- | ---
Disclosure of operating segments [line items] |  |  |  |
Asset retirement obligations | $ 4,327 | $ 3,243 | $ 2,950 | $ 4,221
North America |  |  |  |
Disclosure of operating segments [line items] |  |  |  |
Asset retirement obligations | 1,840 | 1,444 |  |
North Sea |  |  |  |
Disclosure of operating segments [line items] |  |  |  |
Asset retirement obligations | 755 | 837 |  |
Offshore Africa |  |  |  |
Disclosure of operating segments [line items] |  |  |  |
Asset retirement obligations | 245 | 244 |  |
Oil Sands Mining and Upgrading |  |  |  |
Disclosure of operating segments [line items] |  |  |  |
Asset retirement obligations | 1,486 | 717 |  |
Midstream |  |  |  |
Disclosure of operating segments [line items] |  |  |  |
Asset retirement obligations | $ 1 | $ 1 |  |

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