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Related Party Transactions Disclosure of interests in subsidiaries (Details) | 1 Months Ended | 4 Months Ended | 7 Months Ended | 11 Months Ended | 12 Months Ended | 19 Months Ended
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2018 | Jul. 30, 2018 | Jan. 05, 2016 | Nov. 29, 2018 | Nov. 25, 2015 | Jun. 21, 2018 | Dec. 31, 2018 | May 06, 2015 | Jul. 31, 2017
TransAlta Renewables |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) | 60.90% | 61.10% | 66.60% | 61.00% | 76.10% | 64.00% |  | 70.30% | 64.00%
Canada | TransAlta Generation Partnership [Member] |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  | 100.00% |  |
Canada | TransAlta Cogeneration L.P. |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  | 50.01% |  |
Canada | TransAlta Energy Marketing Corp [Member] |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  | 100.00% |  |
Canada | TransAlta Renewables |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  | 60.90% |  |
UNITED STATES | TransAlta Centralia Generation, LLC [Member] |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  | 100.00% |  |
UNITED STATES | TransAlta Energy Marketing (U.S.), Inc [Member] |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  | 100.00% |  |
Australia | TransAlta Energy (Australia). Ptv Ltd [Member] |  |  |  |  |  |  |  |  |
Disclosure of subsidiaries [line items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  |  |  | 100.00% |  |

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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- Definition The proportion of ownership interest in a subsidiary attributable to the entity. [Refer: Subsidiaries [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_17_b_iii&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_16_b_iii&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2017-01-01 -Paragraph 19B -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_19B_c&doctype=Standard -URIDate 2017-03-09 + Details
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