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Risk Management Activities - Net Risk Management Assets and Liabilities (Details) - CAD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Financial Assets |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | $ 696 | $ 677
Not designated as a hedge | Financial Liabilities |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 20 |
Not designated as a hedge | Financial Assets |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | (10)
Commodity risk management |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | 679
Commodity risk management | Financial Assets |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 692 |
Commodity risk management | Current |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 85 | 59
Commodity risk management | Long-term |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 607 | 620
Commodity risk management | Not designated as a hedge |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | (8)
Commodity risk management | Not designated as a hedge | Financial Liabilities |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 16 |
Commodity risk management | Not designated as a hedge | Current |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 15 |
Commodity risk management | Not designated as a hedge | Long-term |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 1 | (8)
Commodity risk management | Not designated as a hedge | Current |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | 0
Other |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | (2)
Other | Financial Assets |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 4 |
Other | Current |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 0 | (3)
Other | Long-term |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 4 | 1
Other | Not designated as a hedge | Financial Liabilities |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | (2)
Other | Not designated as a hedge | Current |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | (3)
Other | Not designated as a hedge | Long-term |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | 1
Other | Not designated as a hedge | Financial Assets |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 4 |
Other | Not designated as a hedge | Current |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 0 |
Other | Not designated as a hedge | Long-term |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 4 |
Cash flow hedges | Designated as a hedge | Financial Assets |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 676 | 687
Cash flow hedges | Commodity risk management | Designated as a hedge |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | 687
Cash flow hedges | Commodity risk management | Designated as a hedge | Financial Assets |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 676 |
Cash flow hedges | Commodity risk management | Designated as a hedge | Current |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 70 | 59
Cash flow hedges | Commodity risk management | Designated as a hedge | Long-term |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 606 | 628
Cash flow hedges | Other | Designated as a hedge |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic |  | 0
Cash flow hedges | Other | Designated as a hedge | Financial Assets |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 0 |
Cash flow hedges | Other | Designated as a hedge | Current |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | 0 | 0
Cash flow hedges | Other | Designated as a hedge | Long-term |  |
Disclosure of detailed information about financial instruments [line items] |  |
Risk exposure associated with instruments sharing characteristic | $ 0 | $ 0

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