Document and Entity Information Document (USD $)	12 Months Ended
	Dec. 31, 2011	Jan. 27, 2012	Jul. 01, 2011
Document Information [Line Items]
Entity Registrant Name	ALTERA CORP
Entity Central Index Key	0000768251
Document Type	10-K
Document Period End Date	Dec. 31, 2011
Amendment Flag	false
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 9,606,716,688
Entity Common Stock, Shares Outstanding (actual number)		322,374,696