Sales (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Disaggregation of Revenue [Line Items]
Sales	$ 34,528	$ 33,021	$ 68,321	$ 63,761
Eliminations
Disaggregation of Revenue [Line Items]
Sales	(549)	(529)	(1,086)	(1,079)
Retail Pharmacy USA | Reportable Segments
Disaggregation of Revenue [Line Items]
Sales	26,257	24,478	51,979	46,967
Retail Pharmacy USA | Reportable Segments | Pharmacy
Disaggregation of Revenue [Line Items]
Sales	18,892	17,208	38,039	33,487
Retail Pharmacy USA | Reportable Segments | Retail
Disaggregation of Revenue [Line Items]
Sales	7,366	7,270	13,940	13,480
Retail Pharmacy International | Reportable Segments
Disaggregation of Revenue [Line Items]
Sales	3,082	3,317	5,982	6,400
Retail Pharmacy International | Reportable Segments | Pharmacy
Disaggregation of Revenue [Line Items]
Sales	1,010	1,095	2,049	2,202
Retail Pharmacy International | Reportable Segments | Retail
Disaggregation of Revenue [Line Items]
Sales	2,072	2,222	3,933	4,198
Pharmaceutical Wholesale | Reportable Segments
Disaggregation of Revenue [Line Items]
Sales	$ 5,738	$ 5,755	$ 11,446	$ 11,473