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Decommissioning and Other Provisions - Change in Decommissioning and Other Provision Balances (Details) - CAD CAD in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Reconciliation of changes in other provisions [abstract] |  |  |
Balance | CAD 343 | CAD 398 |
Liabilities incurred | 22 | 23 |
Liabilities settled | (50) | (59) |
Liabilities disposed | (8) |  |
Increase Through Adjustments Arising From Passage Of Time, Other Provisions, Net Of Receivable | 23 |  |
Accretion of provisions (Note 20) | 21 | 20 | CAD 21
Revisions in estimated cash flows | 42 | 17 |
Revisions in discount rates | 110 | 44 |
Reversals | (4) | (96) |
Change in foreign exchange rates | (8) | (4) |
Balance | 470 | 343 | 398
Decommissioning and restoration |  |  |
Reconciliation of changes in other provisions [abstract] |  |  |
Balance | 293 | 233 |
Liabilities incurred | 3 | 11 |
Liabilities settled | (19) | (23) |
Liabilities disposed | (8) |  |
Increase Through Adjustments Arising From Passage Of Time, Other Provisions, Net Of Receivable | 23 |  |
Accretion of provisions (Note 20) |  | 19 |
Revisions in estimated cash flows | 41 | 12 |
Revisions in discount rates | 110 | 44 |
Reversals | 0 | 0 |
Change in foreign exchange rates | (6) | (3) |
Balance | CAD 437 | 293 | 233
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 | CAD 50 | 165 |
Liabilities incurred | 19 | 12 |
Liabilities settled | (31) | (36) |
Liabilities disposed | 0 |  |
Increase Through Adjustments Arising From Passage Of Time, Other Provisions, Net Of Receivable | 0 |  |
Accretion of provisions (Note 20) |  | 1 |
Revisions in estimated cash flows | 1 | 5 |
Revisions in discount rates | 0 | 0 |
Reversals | (4) | (96) |
Change in foreign exchange rates | (2) | (1) |
Balance | CAD 33 | CAD 50 | CAD 165

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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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- Definition The increase in other provisions through adjustments arising from the passage of time. [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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