Sales (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2019	May 31, 2018
Disaggregation of Revenue [Line Items]
Sales	$ 34,591	$ 34,334	$ 102,912	$ 98,095
Eliminations
Disaggregation of Revenue [Line Items]
Sales	(563)	(543)	(1,649)	(1,622)
Retail Pharmacy USA | Reportable segments
Disaggregation of Revenue [Line Items]
Sales	26,513	25,917	78,491	72,884
Retail Pharmacy USA | Reportable segments | Pharmacy
Disaggregation of Revenue [Line Items]
Sales	19,585	18,790	57,624	52,258
Retail Pharmacy USA | Reportable segments | Retail
Disaggregation of Revenue [Line Items]
Sales	6,928	7,127	20,867	20,626
Retail Pharmacy International | Reportable segments
Disaggregation of Revenue [Line Items]
Sales	2,776	2,995	8,759	9,395
Retail Pharmacy International | Reportable segments | Pharmacy
Disaggregation of Revenue [Line Items]
Sales	1,047	1,111	3,096	3,316
Retail Pharmacy International | Reportable segments | Retail
Disaggregation of Revenue [Line Items]
Sales	1,730	1,884	5,662	6,079
Pharmaceutical Wholesale | Reportable segments
Disaggregation of Revenue [Line Items]
Sales	$ 5,865	$ 5,965	$ 17,311	$ 17,438