Goodwill and other intangible assets - schedule of goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Aug. 31, 2017	Aug. 31, 2016
Goodwill [Roll Forward]
Net book value - Beginning Period	$ 15,527	$ 16,372
Acquisitions	104	23
Sale of business		(4)
Other		0
Currency translation adjustments	1	(864)
Net book value - Ending Period	15,632	15,527
Operating Segments \| Retail Pharmacy USA
Goodwill [Roll Forward]
Net book value - Beginning Period	9,036	8,940
Acquisitions	103	0
Sale of business		(4)
Other		100
Currency translation adjustments	0	0
Net book value - Ending Period	9,139	9,036
Operating Segments \| Retail Pharmacy International
Goodwill [Roll Forward]
Net book value - Beginning Period	3,369	3,898
Acquisitions	0	23
Sale of business		0
Other		(113)
Currency translation adjustments	23	(439)
Net book value - Ending Period	3,392	3,369
Operating Segments \| Pharmaceutical Wholesale
Goodwill [Roll Forward]
Net book value - Beginning Period	3,122	3,534
Acquisitions	1	0
Sale of business		0
Other		13
Currency translation adjustments	(22)	(425)
Net book value - Ending Period	$ 3,101	$ 3,122

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=64834752&loc=SL49117168-202975

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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