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Non-Controlling Interests - Share of Ownership and Equity Participation in TransAlta Renewables (Details) - TransAlta Renewables | 1 Months Ended | 3 Months Ended | 4 Months Ended | 11 Months Ended | 19 Months Ended
--- | --- | --- | --- | --- | ---
Dec. 31, 2018 | Jul. 30, 2018 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Nov. 29, 2018 | Jun. 21, 2018 | Jul. 31, 2017
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Equity participation percentage | 60.90% | 61.10% | 60.40% | 60.50% | 60.60% | 60.80% | 61.00% | 64.00% | 64.00%
Proportion of equity participation in subsidiary | 60.90% | 61.10% | 60.40% | 60.50% | 60.60% | 60.80% | 61.00% | 64.00% | 59.80%

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