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Risk Management Activities - Commodity Risk Management (Details) - Commodity risk management kJ in Billions | Dec. 31, 2019 MWh | Dec. 31, 2019 J | Dec. 31, 2019 kJ | Dec. 31, 2019 MW | Dec. 31, 2018 MWh | Dec. 31, 2018 J | Dec. 31, 2018 kJ | Dec. 31, 2018 MW
--- | --- | --- | --- | --- | --- | --- | --- | ---
Electricity | Cash flow hedges |  |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |  |
Notional amount sold | 222,000 |  |  |  | 2,128,000 |  |  |
Notional amount purchased | 0 |  |  |  | 0 |  |  |
Electricity | Non-Hedges |  |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |  |
Notional amount sold | 16,097,000 |  |  |  | 58,885,000 |  |  |
Notional amount purchased | 7,204,000 |  |  |  | 37,023,000 |  |  |
Natural gas | Non-Hedges |  |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |  |
Notional amount sold |  | 38,062,000 | 80,413 |  |  | 80,413,000 | 74,194 |
Notional amount purchased |  | 55,023,000 | 110,488 |  |  | 110,488,000 | 103,805 |
Transmission | Non-Hedges |  |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |  |
Notional amount sold | 0 |  |  |  | 29,000 |  |  |
Notional amount purchased | 1,818,000 |  |  |  | 11,163,000 |  |  |
Emissions | Non-Hedges |  |  |  |  |  |  |  |
Disclosure of detailed information about hedges [line items] |  |  |  |  |  |  |  |
Notional amount sold | MW |  |  |  | 184,000 |  |  |  | 0
Notional amount purchased | MW |  |  |  | 138,000 |  |  |  | 0

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