Goodwill and other intangible assets - Schedule of Goodwill (Details) $ in Millions	3 Months Ended
Nov. 30, 2018 USD ($)
Goodwill [Roll Forward]
Net book value - Beginning Period	$ 16,914
Acquisitions	6
Currency translation adjustments	(111)
Net book value - Ending Period	16,809
Reportable Segments \| Retail Pharmacy USA
Goodwill [Roll Forward]
Net book value - Beginning Period	10,483
Acquisitions	6
Currency translation adjustments	0
Net book value - Ending Period	10,489
Reportable Segments \| Retail Pharmacy International
Goodwill [Roll Forward]
Net book value - Beginning Period	3,370
Acquisitions	0
Currency translation adjustments	(64)
Net book value - Ending Period	3,306
Reportable Segments \| Pharmaceutical Wholesale
Goodwill [Roll Forward]
Net book value - Beginning Period	3,061
Acquisitions	0
Currency translation adjustments	(47)
Net book value - Ending Period	$ 3,014

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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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.

+ References

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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