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Commitments and Contingencies (Details) $ in Millions, $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2020 CAD ($) | Dec. 31, 2021 CAD ($) | Dec. 31, 2021 USD ($) | Jun. 30, 2021 TJ | Jul. 30, 2015 USD ($)
Disclosure of Commitments [Line Items] |  |  |  |  |
Long-term firm natural gas delivery transportation, amount transferred per day | TJ |  |  |  | 400 |
TransAlta Energy Transition Bill |  | $ 12 |  |  | $ 55
Funded portion of energy bill commitment |  |  | $ 46 |  |
Increase (decrease) in loss contingency accrual, percentage | 15.00% |  |  |  |
Increase (decrease) in loss contingency accrual | $ 3 |  |  |  |
Keephills Unit 1 |  |  |  |  |
Disclosure of Commitments [Line Items] |  |  |  |  |
Estimated financial effect of contingent liabilities | 12 |  |  |  |
Tidewater |  |  |  |  |
Disclosure of Commitments [Line Items] |  |  |  |  |
Long-term firm natural gas delivery transportation, amount transferred per day | TJ |  |  |  | 139 |
Increase (decrease) through modification of contractual cash flows, financial assets | $ (1,300) |  |  |  |
Pioneer Pipeline |  |  |  |  |
Disclosure of Commitments [Line Items] |  |  |  |  |
Long-term firm natural gas delivery transportation, amount transferred per day | TJ |  |  |  | 275 |

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