Goodwill and Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Feb. 29, 2012	Aug. 31, 2011	Feb. 28, 2011
Goodwill [Roll Forward]
Goodwill	$ 1,926
Accumulated Impairment Loss	28
Total	2,078	2,017	1,898
Acquisitions	37	132
Other	24	(13)
Net book Value	2,078	2,017	1,898
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	1,896	1,776	1,617
Accumulated amortization	643	564	496
Net intangible assets	1,253	1,212	1,121
Amortization expense for intangible assets	121		98
Estimated annual intangible assets amortization expense [Abstract]
2012			236
2013			214
2014			181
2015			149
2016			111
All business and intangible asset acquisitions [Member]
Business Acquisition [Line Items]
Purchase price, net of assumed cash	204
Goodwill	37
Intangible assets	125
Crescent Pharmacy Holdings Llc Member
Business Acquisition [Line Items]
Purchase price, net of assumed cash	75
Purchased prescription files [Member]
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	901	913	795
Accumulated amortization	372	338	309
Favorable lease interests [Member]
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	385	385	385
Accumulated amortization	94	76	58
Purchasing and payer contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	308	308	303
Accumulated amortization	106	94	81
Trade Name [Member]
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	188	71	44
Accumulated amortization	22	11	7
Other amortizable intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	4	4	5
Accumulated amortization	2	2	2
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross intangible assets	110	95	85
Accumulated amortization	$ 47	$ 43	$ 39