Exit and disposal activities - Restructuring Costs (Details) - Transformational Cost Management Program - USD ($) $ in Millions	3 Months Ended
	Nov. 30, 2020	Nov. 30, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 83	$ 64
Reportable Segments | Retail Pharmacy USA
Restructuring Cost and Reserve [Line Items]
Restructuring costs	58	49
Reportable Segments | Retail Pharmacy International
Restructuring Cost and Reserve [Line Items]
Restructuring costs	22	9
Reportable Segments | Pharmaceutical Wholesale
Restructuring Cost and Reserve [Line Items]
Restructuring costs	4	6
Lease obligations and other real estate costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	22	1
Lease obligations and other real estate costs | Reportable Segments | Retail Pharmacy USA
Restructuring Cost and Reserve [Line Items]
Restructuring costs	22	1
Lease obligations and other real estate costs | Reportable Segments | Retail Pharmacy International
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	0
Lease obligations and other real estate costs | Reportable Segments | Pharmaceutical Wholesale
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	0
Asset impairments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	4	11
Asset impairments | Reportable Segments | Retail Pharmacy USA
Restructuring Cost and Reserve [Line Items]
Restructuring costs	4	8
Asset impairments | Reportable Segments | Retail Pharmacy International
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	3
Asset impairments | Reportable Segments | Pharmaceutical Wholesale
Restructuring Cost and Reserve [Line Items]
Restructuring costs	0	0
Employee severance and business transition costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	51	40
Employee severance and business transition costs | Reportable Segments | Retail Pharmacy USA
Restructuring Cost and Reserve [Line Items]
Restructuring costs	21	34
Employee severance and business transition costs | Reportable Segments | Retail Pharmacy International
Restructuring Cost and Reserve [Line Items]
Restructuring costs	28	1
Employee severance and business transition costs | Reportable Segments | Pharmaceutical Wholesale
Restructuring Cost and Reserve [Line Items]
Restructuring costs	2	5
Information technology transformation and other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs	6	12
Information technology transformation and other exit costs | Reportable Segments | Retail Pharmacy USA
Restructuring Cost and Reserve [Line Items]
Restructuring costs	10	7
Information technology transformation and other exit costs | Reportable Segments | Retail Pharmacy International
Restructuring Cost and Reserve [Line Items]
Restructuring costs	(6)	4
Information technology transformation and other exit costs | Reportable Segments | Pharmaceutical Wholesale
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 1	$ 1