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Equity method investments - Narrative (Details) - USD ($) $ in Millions			3 Months Ended				9 Months Ended
	Jun. 01, 2021	Jan. 06, 2021	May 31, 2021	Nov. 30, 2020	Sep. 30, 2020	May 31, 2020	May 31, 2021	May 31, 2020	Aug. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity earnings (loss) in AmerisourceBergen			$ 97			$ 243	$ (1,196)	$ 284
Equity earnings (losses)							(577)	297
Gain on sale of equity method investment							$ 290	0
Discontinued Operations, Held-for-sale \| Alliance Healthcare
Schedule of Equity Method Investments [Line Items]
Cash received from disposal	$ 6,275	$ 6,275
Shares issued as part of disposal (in shares)	2,000,000	2,000,000
AmerisourceBergen
Schedule of Equity Method Investments [Line Items]
Outstanding shares owned			56,854,867				56,854,867		56,854,867
Ownership percentage	28.40%		27.70%				27.70%		27.70%
Period of reporting lag							2 months
Equity earnings (losses)				$ (1,373)
Equity investment, exceeded its proportionate share of net assets			$ 4,200				$ 4,200
AmerisourceBergen \| Opiod Litigation
Schedule of Equity Method Investments [Line Items]
Equity earnings (losses)					$ (5,600)
AmerisourceBergen \| Level 1
Schedule of Equity Method Investments [Line Items]
Fair market value of equity investment			6,500				6,500
Other Investments
Schedule of Equity Method Investments [Line Items]
Equity earnings (losses)			575			$ 6	604	$ 5
Option Care Health
Schedule of Equity Method Investments [Line Items]
Equity earnings (losses)			576
Gain on sale of equity method investment			98				290
Option Care Health \| HC Group Holdings I, LLC
Schedule of Equity Method Investments [Line Items]
Gain on sale of equity method investment			1,200
VillageMD
Schedule of Equity Method Investments [Line Items]
Consideration transferred to acquire equity method investments							750
Payments to acquire equity method investments							250
Convertible debt			$ 500				$ 500