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Document and Entity Information (USD $)
 6 Months Ended
Jun. 30, 2014
Jul. 28, 2014
Jun. 30, 2013
Document And Entity Information [Abstract]      
Document Type 10-Q    
Document Period End Date Jun. 30, 2014    
Amendment Flag false    
Entity Registrant Name ALLEGHENY TECHNOLOGIES INCORPORATED    
Entity Central Index Key 0001018963    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Entity Well-known Seasoned Issuer Yes    
Entity Common Stock, Shares Outstanding   108,721,200  
Document Fiscal Year Focus 2014    
Document Fiscal Period Focus Q2    
Entity Public Float     $ 2,800,000,000