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Equity method investments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Nov. 30, 2020	Sep. 30, 2020	Nov. 30, 2019	Aug. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity earnings (losses)	$ (1,350)		$ 4
AmerisourceBergen
Schedule of Equity Method Investments [Line Items]
Outstanding shares owned (in shares)	56,854,867			56,854,867
Ownership percentage	28.00%			28.00%
Period of reporting lag	2 months
Equity earnings (losses)	$ (1,373)
Equity investment, exceeded its proportionate share of net assets	4,300
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	5,900
Other Investments
Schedule of Equity Method Investments [Line Items]
Equity earnings (losses)	$ 23		$ (9)