Exit and disposal activities - restructuring costs (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Transformational cost management program
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	$ 720	$ 432
Transformational cost management program | Reportable Segments | Retail Pharmacy USA
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	486	147
Transformational cost management program | Reportable Segments | Retail Pharmacy International
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	168	130
Transformational cost management program | Reportable Segments | Pharmaceutical Wholesale
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	66	154
Transformational cost management program | Lease obligations and other real estate costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	217	25
Transformational cost management program | Lease obligations and other real estate costs | Reportable Segments | Retail Pharmacy USA
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	204	5
Transformational cost management program | Lease obligations and other real estate costs | Reportable Segments | Retail Pharmacy International
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	10	19
Transformational cost management program | Lease obligations and other real estate costs | Reportable Segments | Pharmaceutical Wholesale
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	2	1
Transformational cost management program | Asset impairments
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	90	260
Transformational cost management program | Asset impairments | Reportable Segments | Retail Pharmacy USA
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	51	95
Transformational cost management program | Asset impairments | Reportable Segments | Retail Pharmacy International
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	21	67
Transformational cost management program | Asset impairments | Reportable Segments | Pharmaceutical Wholesale
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	19	98
Transformational cost management program | Employee severance and business transition costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	295	125
Transformational cost management program | Employee severance and business transition costs | Reportable Segments | Retail Pharmacy USA
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	159	42
Transformational cost management program | Employee severance and business transition costs | Reportable Segments | Retail Pharmacy International
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	95	34
Transformational cost management program | Employee severance and business transition costs | Reportable Segments | Pharmaceutical Wholesale
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	42	49
Transformational cost management program | Information technology transformation and other exit costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	118	22
Transformational cost management program | Information technology transformation and other exit costs | Reportable Segments | Retail Pharmacy USA
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	72	5
Transformational cost management program | Information technology transformation and other exit costs | Reportable Segments | Retail Pharmacy International
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	42	10
Transformational cost management program | Information technology transformation and other exit costs | Reportable Segments | Pharmaceutical Wholesale
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	4	7
Store optimization program
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	53	196	$ 100
Store optimization program | Lease obligations and other real estate costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	22	119	19
Store optimization program | Employee severance and other exit costs
Restructuring Reserve Disclosures [Abstract]
Total restructuring costs	$ 31	$ 77	$ 81