Document and Entity Information - USD ($)	9 Months Ended
	Sep. 30, 2015	Oct. 23, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-Q
Document Period End Date	Sep. 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		109,208,000
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Entity Public Float			$ 4,900,000,000