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Business Segments (Parenthetical) (Detail) - CAD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2019
Segment Reporting Information [Line Items] |  |  |  |
Impairment charge, before tax |  | $ 46 |  |
Plant and equipment under construction | $ 2,149 | 1,553 | $ 1,047 |
Operating Lease, Right-of-Use Asset | 260 |  |  | $ 298
Upstream | Alberta |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Noncash impact | 662 |  |  |
Accounts payable and accrued liabilities |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Non-cash adjustments to accrued liabilities and all other items | 570 |  |  |
United States Exports |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Operating revenues | $ 7,190 | $ 6,661 | 4,392 |
Horn River Development |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Impairment charge, before tax |  |  | 396 |
Mackenzie Gas Project |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Impairment charge, before tax |  |  | $ 379 |

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