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Non-Controlling Interests - Subsidiaries and Operations with Non-Controlling Interests (Details) shares in Millions |  |  |  | 1 Months Ended | 3 Months Ended | 4 Months Ended | 11 Months Ended | 12 Months Ended | 19 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 19, 2018 MW | Aug. 01, 2017 shares | Jul. 31, 2017 | Dec. 31, 2018 | Jul. 30, 2018 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Nov. 29, 2018 | Jun. 21, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Jul. 31, 2017
TransAlta Cogeneration L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  |  |  |  |  |  | 49.99% | 49.99% |
TransAlta Renewables |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  |  |  |  |  |  | 39.60% | 39.10% |
Proportion of equity participation in subsidiary |  |  |  | 60.90% | 61.10% | 60.40% | 60.50% | 60.60% | 60.80% | 61.00% | 64.00% |  |  | 59.80%
TransAlta Renewables | Kent Hills wind farm |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  |  |  |  |  |  | 17.00% |  |
TransAlta Renewables | Australian Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of equity participation in subsidiary |  | 64.00% | 59.80% |  |  |  |  |  |  |  |  |  |  |
TransAlta Renewables | Class B shares | Australian Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares offered for conversion |  | 26.1 |  |  |  |  |  |  |  |  |  |  |  |
TransAlta Renewables | Common shares | Australian Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity securities received upon conversion of shares |  | 26.4 |  |  |  |  |  |  |  |  |  |  |  |
Kent Hills 3 Wind Project |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in contractual power capacity (in megawatts) | MW | 167 |  |  |  |  |  |  |  |  |  |  |  |  |

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