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Decommissioning and Other Provisions - Change in Decommissioning and Other Provision Balances (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Reconciliation of changes in other provisions [abstract] |  |
Balance | $ 470 | $ 343
Liabilities incurred | 22 | 22
Liabilities settled | (41) | (50)
Liabilities disposed |  | (8)
Accretion | (24) | 23
Acquisition of liabilities (Big Level) | 8 |
Revisions in estimated cash flows(2) | 5 | 42
Revisions in discount rates(2) | (37) | 110
Reversals | (5) | (4)
Change in foreign exchange rates | 10 | (8)
Balance | 456 | 470
Decommissioning and restoration |  |
Reconciliation of changes in other provisions [abstract] |  |
Balance | 437 | 293
Liabilities incurred | 5 | 3
Liabilities settled | (31) | (19)
Liabilities disposed |  | (8)
Accretion | (24) | 23
Revisions in estimated cash flows(2) | 2 | 41
Revisions in discount rates(2) | (37) | 110
Reversals | 0 | 0
Change in foreign exchange rates | 7 | (6)
Balance | $ 407 | 437
Decommissioning and restoration | Minimum |  |
Reconciliation of changes in other provisions [abstract] |  |
Use of lower, short-term discount rate (in years) | 5 years |
Increase (decrease) in discount rates, other provisions | (1.60%) |
Decommissioning and restoration | Maximum |  |
Reconciliation of changes in other provisions [abstract] |  |
Use of lower, short-term discount rate (in years) | 15 years |
Increase (decrease) in discount rates, other provisions | (2.10%) |
Other |  |
Reconciliation of changes in other provisions [abstract] |  |
Balance | $ 33 | 50
Liabilities incurred | 17 | 19
Liabilities settled | (10) | (31)
Liabilities disposed |  | 0
Accretion | 0 | 0
Acquisition of liabilities (Big Level) | 8 |
Revisions in estimated cash flows(2) | 3 | 1
Revisions in discount rates(2) | 0 | 0
Reversals | (5) | (4)
Change in foreign exchange rates | 3 | (2)
Balance | $ 49 | $ 33

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- Definition The increase in other provisions resulting from acquisitions through business combinations. [Refer: Business combinations [member]; Other provisions] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 37 -IssueDate 2017-01-01 -Paragraph 84 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2017-03-01&anchor=para_84&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The increase (decrease) in other provisions resulting from a change in discount rate. [Refer: Other provisions] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 37 -IssueDate 2017-01-01 -Paragraph 84 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2017-03-01&anchor=para_84_e&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The increase (decrease) in other provisions resulting from foreign currency exchange rate changes on provisions measured in a currency different from the entity's presentation currency. [Refer: Other provisions] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 37 -IssueDate 2017-01-01 -Paragraph 84 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=37&date=2017-03-01&anchor=para_84&doctype=Standard -URIDate 2017-03-09 + Details
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