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Non-Controlling Interests - Subsidiaries and Operations with Non-Controlling Interests (Details) shares in Millions |  |  | 1 Months Ended | 5 Months Ended | 7 Months Ended | 12 Months Ended | 19 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Aug. 01, 2017 shares | Jul. 31, 2017 | Jan. 05, 2016 | Dec. 31, 2017 | Nov. 25, 2015 | Dec. 31, 2017 | Dec. 31, 2016 MW | May 06, 2015 | Jul. 31, 2017 | May 07, 2015 MW
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 |  |  |  |  |  | 36.00% | 40.20% |  |  |
Proportion of equity participation in subsidiary |  |  | 62.00% | 64.00% | 72.80% |  |  | 70.30% | 59.80% |
TransAlta Renewables | Kent Hills wind farm |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  | 17.00% |  |  |
Capacity of facility (in megawatts) | MW |  |  |  |  |  |  | 150 |  |  |
Australian Assets |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |
Capacity of facility (in megawatts) | MW |  |  |  |  |  |  |  |  |  | 575
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 | shares | 26.1 |  |  |  |  |  |  |  |  |
TransAlta Renewables | Common shares | Australian Assets |  |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |  |
Equity securities received upon conversion of shares | shares | 26.4 |  |  |  |  |  |  |  |  |

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