Equity method investments - additional information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity earnings		$ 382	$ 187	$ 244
AmerisourceBergen
Schedule of Equity Method Investments [Line Items]
Outstanding shares owned (in shares)		56,854,867	56,854,867
Percentage of outstanding common shares owned		28.00%	27.00%
Equity investment, exceeded its proportionate share of net assets		$ 4,400
Others
Schedule of Equity Method Investments [Line Items]
Equity earnings		41	$ 23	$ 53
Guangzhou Pharmaceuticals Corporation
Schedule of Equity Method Investments [Line Items]
Equity method investments, percent of investment sold				30.00%
Equity method investment, amount sold				$ 172
Cumulative translation adjustment loss				8
Premise Health
Schedule of Equity Method Investments [Line Items]
Equity method investment, amount sold	$ 76
Gain disposition of minority equity interest	$ 245
Level 1 | AmerisourceBergen
Schedule of Equity Method Investments [Line Items]
Fair value of assets		5,500	$ 4,700
Other income (expense) | Guangzhou Pharmaceuticals Corporation
Schedule of Equity Method Investments [Line Items]
Equity method investment impairment		$ 86		$ 170