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Fair Values (Derivatives) (Details) - CAD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2016
--- | --- | --- | ---
Assets |  |  |
Total assets | $ 87 | $ 167 |
Liabilities |  |  |
Total liabilities | 370 | 365 |
Fair Value, Measurements, Recurring |  |  |
Assets |  |  |
Total assets | 87 | 167 |
Liabilities |  |  |
Total liabilities | 370 | 365 |
Net assets (liabilities) | (283) | (198) |
Fair Value, Measurements, Recurring | Regulatory deferral |  |  |
Assets |  |  |
Total assets | 28 | 104 |
Liabilities |  |  |
Total liabilities | 78 | 6 |
Fair Value, Measurements, Recurring | Regulatory deferral | Power |  |  |
Assets |  |  |
Total assets | 23 | 2 |
Liabilities |  |  |
Total liabilities | 36 | 1 |
Fair Value, Measurements, Recurring | Regulatory deferral | Coal |  |  |
Assets |  |  |
Total assets | 0 | 70 |
Liabilities |  |  |
Total liabilities | 31 | 1 |
Fair Value, Measurements, Recurring | Regulatory deferral | Heavy fuel oil purchases |  |  |
Assets |  |  |
Total assets | 1 | 1 |
Liabilities |  |  |
Total liabilities |  | 1 |
Fair Value, Measurements, Recurring | Regulatory deferral | Natural gas |  |  |
Assets |  |  |
Total assets | 2 | 2 |
Liabilities |  |  |
Total liabilities | 5 | 3 |
Fair Value, Measurements, Recurring | Regulatory deferral | Foreign exchange forwards |  |  |
Assets |  |  |
Total assets | 2 | 29 |
Liabilities |  |  |
Total liabilities | 6 |  |
Fair Value, Measurements, Recurring | Not Designated as Hedging Instrument |  |  |
Assets |  |  |
Total assets | 1 | 1 |
Fair Value, Measurements, Recurring | Not Designated as Hedging Instrument | Interest rate swaps |  |  |
Assets |  |  |
Total assets | 1 | 1 |
Fair Value, Measurements, Recurring | HFT derivatives |  |  |
Assets |  |  |
Total assets | 58 | 62 |
Liabilities |  |  |
Total liabilities | 291 | 354 |
Fair Value, Measurements, Recurring | HFT derivatives | Power |  |  |
Assets |  |  |
Total assets | 5 | 7 |
Liabilities |  |  |
Total liabilities | 7 | 21 |
Fair Value, Measurements, Recurring | HFT derivatives | Natural gas swaps, futures, forwards, physical contracts | Natural gas |  |  |
Assets |  |  |
Total assets | 53 | 55 |
Liabilities |  |  |
Total liabilities | 284 | 333 |
Fair Value, Measurements, Recurring | HFT derivatives | Interest rate swaps | Power |  |  |
Assets |  |  |
Total assets | 5 |  |
Fair Value, Measurements, Recurring | Level 1 |  |  |
Assets |  |  |
Total assets | 18 | 5 |
Liabilities |  |  |
Total liabilities | 46 | 18 |
Net assets (liabilities) | (28) | (13) |
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral |  |  |
Assets |  |  |
Total assets | 23 | 2 |
Liabilities |  |  |
Total liabilities | 39 | 4 | $ 18
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Power |  |  |
Assets |  |  |
Total assets | 23 | 2 |
Liabilities |  |  |
Total liabilities | 36 | 1 |
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Coal |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Heavy fuel oil purchases |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities |  | 0 |
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Natural gas |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 3 | 3 |
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Foreign exchange forwards |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 0 |  |
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument |  |  |
Assets |  |  |
Total assets | 1 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument | Interest rate swaps |  |  |
Assets |  |  |
Total assets | 1 | 0 |
Fair Value, Measurements, Recurring | Level 1 | HFT derivatives |  |  |
Assets |  |  |
Total assets | (6) | 3 |
Liabilities |  |  |
Total liabilities | 7 | 14 |
Fair Value, Measurements, Recurring | Level 1 | HFT derivatives | Power |  |  |
Assets |  |  |
Total assets | 1 | 2 |
Liabilities |  |  |
Total liabilities |  | 14 |
Fair Value, Measurements, Recurring | Level 1 | HFT derivatives | Natural gas swaps, futures, forwards, physical contracts | Natural gas |  |  |
Assets |  |  |
Total assets | (7) | 1 |
Liabilities |  |  |
Total liabilities | 2 | 0 |
Fair Value, Measurements, Recurring | Level 1 | HFT derivatives | Interest rate swaps | Power |  |  |
Assets |  |  |
Total assets | 1 |  |
Fair Value, Measurements, Recurring | Level 2 |  |  |
Assets |  |  |
Total assets | 54 | 141 |
Liabilities |  |  |
Total liabilities | 75 | 41 |
Net assets (liabilities) | (21) | 100 |
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral |  |  |
Assets |  |  |
Total assets | 5 | 102 |
Liabilities |  |  |
Total liabilities | 39 | 2 |
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral | Power |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral | Coal |  |  |
Assets |  |  |
Total assets | 0 | 70 |
Liabilities |  |  |
Total liabilities | 31 | 1 |
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral | Heavy fuel oil purchases |  |  |
Assets |  |  |
Total assets | 1 | 1 |
Liabilities |  |  |
Total liabilities |  | 1 |
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral | Natural gas |  |  |
Assets |  |  |
Total assets | 2 | 2 |
Liabilities |  |  |
Total liabilities | 2 | 0 |
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral | Foreign exchange forwards |  |  |
Assets |  |  |
Total assets | 2 | 29 |
Liabilities |  |  |
Total liabilities | 6 |  |
Fair Value, Measurements, Recurring | Level 2 | Not Designated as Hedging Instrument |  |  |
Assets |  |  |
Total assets | 0 | 1 |
Fair Value, Measurements, Recurring | Level 2 | Not Designated as Hedging Instrument | Interest rate swaps |  |  |
Assets |  |  |
Total assets | 0 | 1 |
Fair Value, Measurements, Recurring | Level 2 | HFT derivatives |  |  |
Assets |  |  |
Total assets | 49 | 38 |
Liabilities |  |  |
Total liabilities | 35 | 34 |
Fair Value, Measurements, Recurring | Level 2 | HFT derivatives | Power |  |  |
Assets |  |  |
Total assets | 3 | 2 |
Liabilities |  |  |
Total liabilities |  | 6 |
Fair Value, Measurements, Recurring | Level 2 | HFT derivatives | Natural gas swaps, futures, forwards, physical contracts | Natural gas |  |  |
Assets |  |  |
Total assets | 46 | 36 |
Liabilities |  |  |
Total liabilities | 33 | 28 |
Fair Value, Measurements, Recurring | Level 3 |  |  |
Assets |  |  |
Total assets | 15 | 21 |
Liabilities |  |  |
Total liabilities | 249 | 306 |
Net assets (liabilities) | (234) | (285) |
Fair Value, Measurements, Recurring | Level 3 | Regulatory deferral |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Regulatory deferral | Power |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Regulatory deferral | Coal |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Regulatory deferral | Heavy fuel oil purchases |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities |  | 0 |
Fair Value, Measurements, Recurring | Level 3 | Regulatory deferral | Natural gas |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Regulatory deferral | Foreign exchange forwards |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Liabilities |  |  |
Total liabilities | 0 |  |
Fair Value, Measurements, Recurring | Level 3 | Not Designated as Hedging Instrument |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Not Designated as Hedging Instrument | Interest rate swaps |  |  |
Assets |  |  |
Total assets | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives |  |  |
Assets |  |  |
Total assets | 15 | 21 |
Liabilities |  |  |
Total liabilities | 249 | 306 |
Net assets (liabilities) | (234) | (285) |
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Power |  |  |
Assets |  |  |
Total assets | 1 | 3 |
Liabilities |  |  |
Total liabilities |  | 1 |
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Natural gas |  |  |
Assets |  |  |
Total assets | 9 | 8 |
Liabilities |  |  |
Total liabilities | 228 | 286 |
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Energy Related derivative | Natural gas |  |  |
Assets |  |  |
Total assets | 5 | 10 |
Liabilities |  |  |
Total liabilities | 21 | 19 |
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Natural gas swaps, futures, forwards, physical contracts | Natural gas |  |  |
Assets |  |  |
Total assets | 14 | 18 |
Liabilities |  |  |
Total liabilities | $ 249 | $ 305 |

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