Equity method investments - additional information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity earnings		$ 187	$ 245	$ 143
Equity investment, noncontrolling interest		$ 411	$ 445
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		27.00%	26.00%
Equity investment, exceeded its proportionate share of net assets		$ 4,400
Others
Schedule of Equity Method Investments [Line Items]
Equity earnings		23	$ 53	$ 8
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		$ 4,700	5,100
Other income (expense) | Guangzhou Pharmaceuticals Corporation
Schedule of Equity Method Investments [Line Items]
Equity method investment impairment			$ 170