Segment reporting (Details) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2020 USD ($)	May 31, 2019 USD ($)	May 31, 2020 USD ($) segment	May 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Sales	$ 34,631	$ 34,591	$ 104,791	$ 102,912
Adjusted operating income	919	1,717	4,085	5,384
Impairment of goodwill and intangible assets	(2,001)	0	(2,001)	0
Transformational cost management	(315)	(86)	(524)	(265)
Acquisition-related amortization	(112)	(127)	(348)	(373)
Acquisition-related costs	(68)	(80)	(291)	(228)
LIFO provision	(29)	(29)	(90)	(77)
Store damage and inventory losses	(75)	0	(75)	0
Store optimization	(10)	(49)	(49)	(99)
Adjustments to equity earnings (loss) in AmerisourceBergen	105	(137)	(47)	(191)
Certain legal and regulatory accruals and settlements	0	(7)	0	(31)
Operating income (loss)	(1,584)	1,203	662	4,120
Reportable Segments | Retail Pharmacy USA
Segment Reporting Information [Line Items]
Sales	27,357	26,513	80,734	78,491
Adjusted operating income	792	1,286	3,215	4,119
Reportable Segments | Retail Pharmacy International
Segment Reporting Information [Line Items]
Sales	1,903	2,776	7,704	8,759
Adjusted operating income	(143)	165	133	553
Reportable Segments | Pharmaceutical Wholesale
Segment Reporting Information [Line Items]
Sales	5,899	5,865	17,971	17,311
Adjusted operating income	271	265	735	710
Eliminations
Segment Reporting Information [Line Items]
Sales	(527)	(563)	(1,618)	(1,649)
Adjusted operating income	$ 0	$ 1	$ 2	$ 1