Document and Entity Information - shares	6 Months Ended
	Feb. 17, 2019	Mar. 06, 2019
Document and Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Feb. 17, 2019
Document Fiscal Year Focus	2019
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 Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		439,880,257