XML 49 R1.htm IDEA: XBRL DOCUMENT v3.2.0.727
Document and Entity Information - USD ($)
 6 Months Ended
Jun. 30, 2015
Jul. 24, 2015
Jun. 30, 2014
Document And Entity Information [Abstract]      
Document Type 10-Q    
Document Period End Date Jun. 30, 2015    
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   109,209,729  
Document Fiscal Year Focus 2015    
Document Fiscal Period Focus Q2    
Entity Public Float     $ 4,900,000,000