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Fair Value Measurements (Derivatives) (Details) - CAD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Assets |  |
Total assets | $ 98 | $ 87
Liabilities |  |
Total liabilities | 338 | 370
Fair Value, Measurements, Recurring |  |
Assets |  |
Total assets | 98 | 87
Liabilities |  |
Total liabilities | 338 | 370
Net assets (liabilities) | (240) | (283)
Fair Value, Measurements, Recurring | Cash flow hedges |  |
Assets |  |
Total assets | 1 |
Liabilities |  |
Total liabilities |  | 1
Fair Value, Measurements, Recurring | Foreign exchange forwards |  |
Assets |  |
Total assets | 15 |
Fair Value, Measurements, Recurring | Foreign exchange forwards | Cash flow hedges |  |
Liabilities |  |
Total liabilities |  | 1
Fair Value, Measurements, Recurring | Interest rate hedges | Cash flow hedges |  |
Assets |  |
Total assets | 1 |
Fair Value, Measurements, Recurring | Equity derivatives |  |
Assets |  |
Total assets |  | 1
Liabilities |  |
Total liabilities | 1 |
Fair Value, Measurements, Recurring | Other |  |
Liabilities |  |
Total liabilities | 1 |
Fair Value, Measurements, Recurring | Regulatory deferral |  |
Assets |  |
Total assets | 14 | 28
Liabilities |  |
Total liabilities | 62 | 78
Fair Value, Measurements, Recurring | Regulatory deferral | Coal |  |
Liabilities |  |
Total liabilities | 4 | 31
Fair Value, Measurements, Recurring | Regulatory deferral | Power |  |
Assets |  |
Total assets | 9 | 23
Liabilities |  |
Total liabilities | 33 | 36
Fair Value, Measurements, Recurring | Regulatory deferral | Heavy fuel oil purchases |  |
Assets |  |
Total assets | 2 | 1
Liabilities |  |
Total liabilities | 6 |
Fair Value, Measurements, Recurring | Regulatory deferral | Natural gas |  |
Assets |  |
Total assets | 3 | 2
Liabilities |  |
Total liabilities | 2 | 5
Fair Value, Measurements, Recurring | Regulatory deferral | Foreign exchange forwards |  |
Assets |  |
Total assets |  | 2
Liabilities |  |
Total liabilities | 17 | 6
Fair Value, Measurements, Recurring | Not Designated as Hedging Instrument |  |
Assets |  |
Total assets | 15 | 1
Fair Value, Measurements, Recurring | Not Designated as Hedging Instrument | Interest rate hedges |  |
Assets |  |
Total assets |  | 1
Fair Value, Measurements, Recurring | HFT derivatives |  |
Assets |  |
Total assets | 68 | 58
Liabilities |  |
Total liabilities | 275 | 291
Fair Value, Measurements, Recurring | HFT derivatives | Power |  |
Assets |  |
Total assets | 7 | 5
Liabilities |  |
Total liabilities | 7 | 7
Fair Value, Measurements, Recurring | HFT derivatives | Natural gas swaps, futures, forwards, physical contracts and related transportation | Natural gas |  |
Assets |  |
Total assets | 61 | 53
Liabilities |  |
Total liabilities | 268 | 284
Fair Value, Measurements, Recurring | Level 1 |  |
Assets |  |
Total assets | 16 | 18
Liabilities |  |
Total liabilities | 42 | 46
Net assets (liabilities) | (26) | (28)
Fair Value, Measurements, Recurring | Level 1 | Cash flow hedges |  |
Assets |  |
Total assets | 1 |
Liabilities |  |
Total liabilities |  | 0
Fair Value, Measurements, Recurring | Level 1 | Foreign exchange forwards |  |
Assets |  |
Total assets | 0 |
Fair Value, Measurements, Recurring | Level 1 | Foreign exchange forwards | Cash flow hedges |  |
Liabilities |  |
Total liabilities |  | 0
Fair Value, Measurements, Recurring | Level 1 | Interest rate hedges | Cash flow hedges |  |
Assets |  |
Total assets | 1 |
Fair Value, Measurements, Recurring | Level 1 | Equity derivatives |  |
Assets |  |
Total assets |  | 1
Liabilities |  |
Total liabilities | 1 |
Fair Value, Measurements, Recurring | Level 1 | Other |  |
Liabilities |  |
Total liabilities | 1 |
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral |  |
Assets |  |
Total assets | 11 | 23
Liabilities |  |
Total liabilities | 36 | 39
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Coal |  |
Liabilities |  |
Total liabilities | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Power |  |
Assets |  |
Total assets | 9 | 23
Liabilities |  |
Total liabilities | 33 | 36
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Heavy fuel oil purchases |  |
Assets |  |
Total assets | 0 | 0
Liabilities |  |
Total liabilities | 3 |
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Natural gas |  |
Assets |  |
Total assets | 2 | 0
Liabilities |  |
Total liabilities | 0 | 3
Fair Value, Measurements, Recurring | Level 1 | Regulatory deferral | Foreign exchange forwards |  |
Assets |  |
Total assets |  | 0
Liabilities |  |
Total liabilities | 0 | 0
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument |  |
Assets |  |
Total assets | 0 | 1
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument | Interest rate hedges |  |
Assets |  |
Total assets |  | 1
Fair Value, Measurements, Recurring | Level 1 | HFT derivatives |  |
Assets |  |
Total assets | 4 | (6)
Liabilities |  |
Total liabilities | 5 | 7
Fair Value, Measurements, Recurring | Level 1 | HFT derivatives | Power |  |
Assets |  |
Total assets | 3 | 1
Liabilities |  |
Total liabilities | 4 | 5
Fair Value, Measurements, Recurring | Level 1 | HFT derivatives | Natural gas swaps, futures, forwards, physical contracts and related transportation | Natural gas |  |
Assets |  |
Total assets | 1 | (7)
Liabilities |  |
Total liabilities | 1 | 2
Fair Value, Measurements, Recurring | Level 2 |  |
Assets |  |
Total assets | 68 | 54
Liabilities |  |
Total liabilities | 38 | 75
Net assets (liabilities) | 30 | (21)
Fair Value, Measurements, Recurring | Level 2 | Cash flow hedges |  |
Assets |  |
Total assets | 0 |
Liabilities |  |
Total liabilities |  | 1
Fair Value, Measurements, Recurring | Level 2 | Foreign exchange forwards |  |
Assets |  |
Total assets | 15 |
Fair Value, Measurements, Recurring | Level 2 | Foreign exchange forwards | Cash flow hedges |  |
Liabilities |  |
Total liabilities |  | 1
Fair Value, Measurements, Recurring | Level 2 | Interest rate hedges | Cash flow hedges |  |
Assets |  |
Total assets | 0 |
Fair Value, Measurements, Recurring | Level 2 | Equity derivatives |  |
Assets |  |
Total assets |  | 0
Liabilities |  |
Total liabilities | 0 |
Fair Value, Measurements, Recurring | Level 2 | Other |  |
Liabilities |  |
Total liabilities | 0 |
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral |  |
Assets |  |
Total assets | 3 | 5
Liabilities |  |
Total liabilities | 26 | 39
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral | Coal |  |
Liabilities |  |
Total liabilities | 4 | 31
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 | Heavy fuel oil purchases |  |
Assets |  |
Total assets | 2 | 1
Liabilities |  |
Total liabilities | 3 |
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral | Natural gas |  |
Assets |  |
Total assets | 1 | 2
Liabilities |  |
Total liabilities | 2 | 2
Fair Value, Measurements, Recurring | Level 2 | Regulatory deferral | Foreign exchange forwards |  |
Assets |  |
Total assets |  | 2
Liabilities |  |
Total liabilities | 17 | 6
Fair Value, Measurements, Recurring | Level 2 | Not Designated as Hedging Instrument |  |
Assets |  |
Total assets | 15 | 0
Fair Value, Measurements, Recurring | Level 2 | Not Designated as Hedging Instrument | Interest rate hedges |  |
Assets |  |
Total assets |  | 0
Fair Value, Measurements, Recurring | Level 2 | HFT derivatives |  |
Assets |  |
Total assets | 50 | 49
Liabilities |  |
Total liabilities | 12 | 35
Fair Value, Measurements, Recurring | Level 2 | HFT derivatives | Power |  |
Assets |  |
Total assets | 2 | 3
Liabilities |  |
Total liabilities | 2 | 2
Fair Value, Measurements, Recurring | Level 2 | HFT derivatives | Natural gas swaps, futures, forwards, physical contracts and related transportation | Natural gas |  |
Assets |  |
Total assets | 48 | 46
Liabilities |  |
Total liabilities | 10 | 33
Fair Value, Measurements, Recurring | Level 3 |  |
Assets |  |
Total assets | 14 | 15
Liabilities |  |
Total liabilities | 258 | 249
Net assets (liabilities) | (244) | (234)
Fair Value, Measurements, Recurring | Level 3 | Cash flow hedges |  |
Assets |  |
Total assets | 0 |
Liabilities |  |
Total liabilities |  | 0
Fair Value, Measurements, Recurring | Level 3 | Foreign exchange forwards |  |
Assets |  |
Total assets | 0 |
Fair Value, Measurements, Recurring | Level 3 | Foreign exchange forwards | Cash flow hedges |  |
Liabilities |  |
Total liabilities |  | 0
Fair Value, Measurements, Recurring | Level 3 | Interest rate hedges | Cash flow hedges |  |
Assets |  |
Total assets | 0 |
Fair Value, Measurements, Recurring | Level 3 | Equity derivatives |  |
Assets |  |
Total assets |  | 0
Liabilities |  |
Total liabilities | 0 |
Fair Value, Measurements, Recurring | Level 3 | Other |  |
Liabilities |  |
Total liabilities | 0 |
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 | Coal |  |
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 | 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
Liabilities |  |
Total liabilities | 0 | 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 hedges |  |
Assets |  |
Total assets |  | 0
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives |  |
Assets |  |
Total assets | 14 | 15
Liabilities |  |
Total liabilities | 258 | 249
Net assets (liabilities) | (244) | (234)
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Power |  |
Assets |  |
Total assets | 2 | 1
Liabilities |  |
Total liabilities | 1 | 0
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Natural gas |  |
Assets |  |
Total assets | 18 | 9
Liabilities |  |
Total liabilities | 226 | 228
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Energy Related derivative | Power |  |
Assets |  |
Total assets | 1 |
Liabilities |  |
Total liabilities | 1 |
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Energy Related derivative | Natural gas |  |
Assets |  |
Total assets | (6) | 5
Liabilities |  |
Total liabilities | 30 | 21
Fair Value, Measurements, Recurring | Level 3 | HFT derivatives | Natural gas swaps, futures, forwards, physical contracts and related transportation | Natural gas |  |
Assets |  |
Total assets | 12 | 14
Liabilities |  |
Total liabilities | $ 257 | $ 249

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