Goodwill and other intangible assets - Schedule of Goodwill (Details) $ in Millions	3 Months Ended
Nov. 30, 2020 USD ($)
Goodwill [Roll Forward]
Net book value - beginning balance	$ 15,268
Acquisitions	4
Currency translation adjustments	27
Net book value - ending balance	15,299
Reportable Segments \| Retail Pharmacy USA
Goodwill [Roll Forward]
Net book value - beginning balance	10,553
Acquisitions	1
Currency translation adjustments	0
Net book value - ending balance	10,554
Reportable Segments \| Retail Pharmacy International
Goodwill [Roll Forward]
Net book value - beginning balance	1,593
Acquisitions	0
Currency translation adjustments	18
Net book value - ending balance	1,612
Reportable Segments \| Pharmaceutical Wholesale
Goodwill [Roll Forward]
Net book value - beginning balance	3,122
Acquisitions	3
Currency translation adjustments	9
Net book value - ending balance	$ 3,133

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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10)(1))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: 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=120320667&loc=SL49117168-202975

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

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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
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-Topic 350
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-Section 50
-Paragraph 1
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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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 350
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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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