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Risk Management Activities - Hedging Instruments (Details) $ in Thousands, $ in Thousands, $ in Millions, kJ in Billions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 CAD ($) MWh kJ | Dec. 31, 2017 CAD ($) MWh kJ | Dec. 31, 2016 CAD ($) | Dec. 31, 2018 USD ($) MWh kJ | Dec. 31, 2018 AUD ($) MWh kJ | Dec. 31, 2017 USD ($) MWh kJ
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Collateral paid (Note 15) | $ 105,000 | $ 67,000 |  |  |  |
Notional amount | 3,234,000 | 3,664,000 |  |  |  |
Fair value asset | 10,000 | 30,000 |  |  |  |
Unrealized pre-tax gains (losses) | 4,000 | $ 2,000 | $ 0 |  |  |
Borrowings subject to floating interest rates |  | 14.44032% | 6.00% |  |  | 14.44032%
Gains (losses) on exchange differences on translation, net of tax | $ 43,000 | $ (25,000) |  |  |  |
Electricity | Non-Hedges | Commodity risk management |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount sold | MWh | 58,885,000 | 14,688,000 |  | 58,885,000 | 58,885,000 | 14,688,000
Notional amount purchased | MWh | 37,023,000 | 7,348,000 |  | 37,023,000 | 37,023,000 | 7,348,000
Electricity | Cash flow hedges | Commodity risk management |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount sold | MWh | 2,128,000 | 1,997,000 |  | 2,128,000 | 2,128,000 | 1,997,000
Notional amount purchased | MWh | 0 | 44,000 |  | 0 | 0 | 44,000
Long-term debt | Net investment hedges |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount |  |  |  | $ 400,000 |  | $ 480,000
Long-term debt | Fair value hedges | Interest rate risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount |  |  |  | 50,000 |  | $ 50,000
Physical power sales | Cash flow hedges | Commodity risk management |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount |  |  |  | $ 400 |  |
Fair value asset | $ 687,000 |  |  |  |  |
Notional amount purchased | MWh | 23,000 |  |  | 23,000 | 23,000 |
Gain (loss) on hedge ineffectiveness | $ 60,000 |  |  |  |  |
Reserve of cash flow hedges | 508,000 |  |  |  |  |
Foreign Exchange Forward Contracts - foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Fair value asset |  | $ 11,000 |  |  |  |
Fair value liability | 5,000 | 9,000 |  |  |  |
Foreign Exchange Forward Contracts - foreign-denominated debt | Discontinued Hedge Positions | Currency risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount sold | 124,000 |  |  |  |  |
Notional amount purchased |  | 230 |  | $ 100,000 |  |
Fair value asset | 10,000 |  |  |  |  |
Fair value liability |  | 4,000 |  |  |  |
Cross-Currency Swaps - foreign-denominated debt | Discontinued Hedge Positions | Currency risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount sold | 0 |  |  |  |  |
Notional amount purchased |  | 270 |  | $ 0 |  |
Fair value asset | $ 0 | $ 35,000 |  |  |  |
Natural gas | Non-Hedges | Commodity risk management |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount sold | kJ | 80,413 | 74,194 |  | 80,413 | 80,413 | 74,194
Notional amount purchased | kJ | 110,488 | 103,805 |  | 110,488 | 110,488 | 103,805
Transmission | Non-Hedges | Commodity risk management |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount sold | MWh | 29,000 | 1,000 |  | 29,000 | 29,000 | 1,000
Notional amount purchased | MWh | 11,163,000 | 3,455,000 |  | 11,163,000 | 11,163,000 | 3,455,000
Foreign-denominated debt | Net Investment Hedge | Currency risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Fair value asset | $ 1,000 |  |  |  |  |
Gain (loss) on hedge ineffectiveness | 41,000 |  |  |  |  |
Minimum | Foreign Exchange Forward Contracts - foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount purchased | 214,000 | $ 157,000 |  |  |  |
Maximum | Foreign Exchange Forward Contracts - foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount purchased | 205,000 | 104,000 |  |  |  |
Fair value liability | 7,000 |  |  |  |  |
U.S. Dollars | Foreign Exchange Forward Contracts - foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount sold |  |  |  | $ 164,000 |  |
Australia, Dollars | Foreign Exchange Forward Contracts - foreign-denominated receipts/expenditures | Discontinued Hedge Positions | Currency risk |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Notional amount sold |  |  |  |  | $ 218 |
Reserve of exchange differences on translation |  |  |  |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |  |  |  |
Gains (losses) on exchange differences on translation, net of tax | $ (84,000) | $ 89,000 |  |  |  |

X
- Definition The amount of current non-cash collateral assets (such as debt or equity instruments) provided to a transferee, for which the transferee has the right by contract or custom to sell or repledge the collateral. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Expiry date 2018-01-01 -Name IAS -Number 39 -IssueDate 2017-01-01 -Paragraph 37 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=39&date=2017-03-02&anchor=para_37_a&doctype=Standard&book=B -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 9 -IssueDate 2017-01-01 -Paragraph 3.2.23 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=9&date=2017-03-01&anchor=para_3.2.23_a&doctype=Standard -URIDate 2017-03-09 + Details
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