Exit and disposal activities - restructuring costs (Details) - Transformational cost management program - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2022	Aug. 31, 2021	Aug. 31, 2020
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	$ 690	$ 335	$ 665
Reportable Segments | U.S. Retail Pharmacy
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	546	217	444
Reportable Segments | International
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	118	72	163
Corporate and Other
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	25	46	58
Lease obligations and other real estate costs
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	249	108	215
Lease obligations and other real estate costs | Reportable Segments | U.S. Retail Pharmacy
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	247	103	191
Lease obligations and other real estate costs | Reportable Segments | International
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	2	6	9
Lease obligations and other real estate costs | Corporate and Other
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	0	0	14
Asset impairments
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	190	24	72
Asset impairments | Reportable Segments | U.S. Retail Pharmacy
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	132	15	51
Asset impairments | Reportable Segments | International
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	58	9	19
Asset impairments | Corporate and Other
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	0	0	2
Employee severance and business transition costs
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	210	165	270
Employee severance and business transition costs | Reportable Segments | U.S. Retail Pharmacy
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	156	79	132
Employee severance and business transition costs | Reportable Segments | International
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	29	40	93
Employee severance and business transition costs | Corporate and Other
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	25	45	45
Information technology transformation and other exit costs
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	40	38	108
Information technology transformation and other exit costs | Reportable Segments | U.S. Retail Pharmacy
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	12	20	70
Information technology transformation and other exit costs | Reportable Segments | International
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	29	17	42
Information technology transformation and other exit costs | Corporate and Other
Restructuring Reserve Disclosures [Abstract]
Total pre-tax exit and disposal charges	$ 0	$ 0	$ (4)