Equity And Comprehensive Income (Components Of Equity And Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Feb. 12, 2012	Feb. 13, 2011	Feb. 12, 2012	Feb. 13, 2011
Equity And Comprehensive Income [Line Items]
Equity, Beginning			$ 12,573	$ 10,930
Initial consolidation of noncontrolling interest in Costco Mexico				357
Unrealized gain/(loss) on short-term investments, net of tax	0	(4)	(1)	(3)
Foreign currency translation adjustment and other	132	86	(76)	263
Net income	412	369	740	701
Total comprehensive income	544	451	663	961
Stock-based compensation	58	52	134	109
Stock options exercised including tax effects			49	236
Release of vested restricted stock units (RSUs) including tax effects			(74)	(45)
Conversion of convertible notes			1
Repurchases of common stock	(145)	(95)	(318)	(245)
Cash dividends			(209)	(179)
Equity, Ending	12,819	12,124	12,819	12,124
Unrealized (loss) gain on short-term investments, tax	0	2	1	2
Attributable To Costco [Member]
Equity And Comprehensive Income [Line Items]
Equity, Beginning			12,002	10,829
Initial consolidation of noncontrolling interest in Costco Mexico				0
Unrealized gain/(loss) on short-term investments, net of tax			(1)	(3)
Foreign currency translation adjustment and other			(66)	221
Net income			714	660
Total comprehensive income			647	878
Stock-based compensation			134	109
Stock options exercised including tax effects			49	236
Release of vested restricted stock units (RSUs) including tax effects			(74)	(45)
Conversion of convertible notes			1
Repurchases of common stock			(318)	(245)
Cash dividends			(209)	(179)
Equity, Ending	12,232	11,583	12,232	11,583
Noncontrolling Interests [Member]
Equity And Comprehensive Income [Line Items]
Equity, Beginning			571	101
Initial consolidation of noncontrolling interest in Costco Mexico				357
Unrealized gain/(loss) on short-term investments, net of tax			0	0
Foreign currency translation adjustment and other			(10)	42
Net income			26	41
Total comprehensive income			16	83
Stock-based compensation			0	0
Stock options exercised including tax effects			0	0
Release of vested restricted stock units (RSUs) including tax effects			0	0
Conversion of convertible notes			0
Repurchases of common stock			0	0
Cash dividends			0	0
Equity, Ending	$ 587	$ 541	$ 587	$ 541