Cover - USD ($)	12 Months Ended
	Aug. 30, 2020	Sep. 29, 2020	Feb. 16, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Aug. 30, 2020
Document Fiscal Year Focus	2020
Entity File Number	0-20355
Entity Incorporation, State or Country Code	WA
Entity Tax Identification Number	91-1223280
Entity Address, Address Line One	999 Lake Drive
Entity Address, City or Town	Issaquah
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	98027
City Area Code	425
Local Phone Number	313-8100
Title of 12(b) Security	Common Stock, $.01 Par Value
Trading Symbol	COST
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Registrant Name	COSTCO WHOLESALE CORP /NEW
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Shell Company	false
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		441,228,027
Entity Public Float			$ 140,245,657,604
Document Fiscal Period Focus	FY
Entity Central Index Key	0000909832
Current Fiscal Year End Date	--08-30
ICFR Auditor Attestation Flag	true