Document and Entity Information	6 Months Ended
	Feb. 17, 2013	Mar. 13, 2013
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Feb. 17, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q2
Trading Symbol	COST
Entity Registrant Name	COSTCO WHOLESALE CORP /NEW
Entity Central Index Key	0000909832
Current Fiscal Year End Date	--09-01
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		436,371,394