Document and Entity Information - USD ($)	12 Months Ended
	Sep. 01, 2019	Oct. 03, 2019	Feb. 17, 2019
Document and Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 01, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q4
Trading Symbol	COST
Entity Registrant Name	COSTCO WHOLESALE CORP /NEW
Entity Central Index Key	0000909832
Current Fiscal Year End Date	--09-01
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		439,656,950
Entity Public Float			$ 95,005,703,244