XML 12 R1.htm IDEA: XBRL DOCUMENT v3.7.0.1
Document and Entity Information - USD ($)
 3 Months Ended
Mar. 31, 2017
Apr. 21, 2017
Jun. 30, 2016
Document And Entity Information [Abstract]      
Document Type 10-Q    
Document Period End Date Mar. 31, 2017    
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   108,822,255  
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus Q1    
Entity Public Float     $ 1,400,000,000