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Equity method investments - additional information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Schedule of Equity Method Investments [Line Items]
Equity earnings		$ 245	$ 143	$ 81
Equity investment, noncontrolling interest		$ 445	$ 204
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		26.00%	26.00%
Equity investment, exceeded its proportionate share of net assets		$ 4,300
Ownership percentage		26.00%	26.00%
Others
Schedule of Equity Method Investments [Line Items]
Equity earnings		$ 53	$ 8	$ 44
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		5,100
Other income (expense) \| Guangzhou Pharmaceuticals Corporation
Schedule of Equity Method Investments [Line Items]
Equity method investment impairment		$ 170