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Document and Entity Information Document
CAD in Thousands
 12 Months Ended
Dec. 31, 2016
CAD
shares
Document And Entity Information [Abstract]  
Document Type 40-F
Document Period End Date Dec. 31, 2017
Amendment Flag false
Entity Registrant Name TransAlta Corporation
Entity Central Index Key 0001144800
Entity Current Reporting Status Yes
Current Fiscal Year End Date --12-31
Document Fiscal Year Focus 2017
Document Fiscal Period Focus FY
Entity Voluntary Filers No
Entity Well-Known Seasoned Issuer No
Entity Common Shares Outstanding | shares 287,903,467
Entity Public Float | CAD CAD 0