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Financial Instruments Fair value of the commodity risk management assets and liabilities by classification level (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Change in foreign exchange rates | $ (15) | $ (1) | $ (5)
Gains recognized in OCI | (57) | (138) | (105)
Total gains included in earnings before income taxes | (9) | 136 | 271
Other |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Risk exposure associated with instruments sharing characteristic |  | 34 |
Commodity risk management |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Risk exposure associated with instruments sharing characteristic |  | 728 |
Recurring fair value measurement | Level I |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Risk exposure associated with instruments sharing characteristic | 3 | (1) |
Recurring fair value measurement | Level 2 of fair value hierarchy [member] |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Risk exposure associated with instruments sharing characteristic | (19) | (42) |
Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Risk exposure associated with instruments sharing characteristic | 695 | 771 | 758
Market price changes | (132) | (67) |
Change in foreign exchange rates | 72 | (52) |
Transfers into Level 3 of fair value hierarchy, assets | (4) | 1 |
Recurring fair value measurement | Level III | Other |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Risk exposure associated with instruments sharing characteristic | (2) | 34 |
Non-recurring fair value measurement [member] | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Gains recognized in OCI | 60 | 50 |
Total gains included in earnings before income taxes | 90 | 86 |
Unrealized gains included in earnings before income taxes relating to met assets held | (42) | 19 |
Fair value hedges [member] | Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Risk exposure associated with instruments sharing characteristic | 689 | 719 | 726
Market price changes | (90) | (57) |
Change in foreign exchange rates | 67 | (50) |
Transfers into Level 3 of fair value hierarchy, assets | 0 | 0 |
Fair value hedges [member] | Non-recurring fair value measurement [member] | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Gains recognized in OCI | 60 | 50 |
Total gains included in earnings before income taxes | 90 | 57 |
Unrealized gains included in earnings before income taxes relating to met assets held | 0 | 0 |
Non-Hedges | Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Risk exposure associated with instruments sharing characteristic | 6 | 52 | $ 32
Market price changes | (42) | (10) |
Change in foreign exchange rates | 5 | (2) |
Transfers into Level 3 of fair value hierarchy, assets | (4) | 1 |
Non-Hedges | Non-recurring fair value measurement [member] | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Gains recognized in OCI | 0 | 0 |
Total gains included in earnings before income taxes | 0 | 29 |
Unrealized gains included in earnings before income taxes relating to met assets held | (42) | 19 |
Derivative Instruments, Existing Contracts [Member] | Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Market price changes | (16) | 98 |
Derivative Instruments, Existing Contracts [Member] | Fair value hedges [member] | Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Market price changes | (7) | 100 |
Derivative Instruments, Existing Contracts [Member] | Non-Hedges | Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Market price changes | (9) | (2) |
Derivative Instruments, New Contracts [Member] | Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Market price changes | 4 | 33 |
Derivative Instruments, New Contracts [Member] | Fair value hedges [member] | Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Market price changes | 0 | 0 |
Derivative Instruments, New Contracts [Member] | Non-Hedges | Recurring fair value measurement | Level III |  |  |
Disclosure of risk management strategy related to hedge accounting [line items] |  |  |
Market price changes | $ 4 | $ 33 |

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- Definition The gain (loss) recognised in other comprehensive income on hedge ineffectiveness. [Refer: Gain (loss) on hedge ineffectiveness] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 24C -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_24C_a_i&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The gains (losses) recognised in other comprehensive income on cash flow hedges, before tax. [Refer: Cash flow hedges [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 23 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-02&anchor=para_23_c&doctype=Standard&book=B -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 91 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_91_b&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of exchange differences recognised in profit or loss that arise from foreign currency transactions, excluding those arising on financial instruments measured at fair value through profit or loss in accordance with IFRS 9. [Refer: At fair value [member]; Financial instruments, class [member]] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 7 -IssueDate 2017-01-01 -Section A Statement of cash flows for an entity other than a financial institution -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2017-03-01&anchor=sect_AStatementofcashflowsforanentityotherthanafinancialinstitution&doctype=Illustrative%20Examples -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 21 -IssueDate 2017-01-01 -Paragraph 52 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=21&date=2017-03-01&anchor=para_52_a&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The increase (decrease) in exposure to credit risk on loan commitments and financial guarantee contracts. [Refer: Exposure to credit risk on loan commitments and financial guarantee contracts] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 35H -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_35H&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 35I -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_35I&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The amount of risk exposure associated with financial instruments with a shared characteristic that identifies a concentration of risks. [Refer: Financial instruments, class [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph B8 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_B8_c&doctype=Appendix&seq=2 -URIDate 2017-03-09 + Details
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