Document and Entity Information - shares	8 Months Ended
	May 12, 2019	May 29, 2019
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	May 12, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	COST
Entity Registrant Name	COSTCO WHOLESALE CORP /NEW
Entity Central Index Key	0000909832
Current Fiscal Year End Date	--09-01
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		439,789,186