Retirement benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2019	May 31, 2018
Components of net periodic benefit costs [Abstract]
Employer cash contributions to defined benefit pension plans			$ 28
Employee expected additional contribution in current fiscal year			6
Boots and other pension plans
Components of net periodic benefit costs [Abstract]
Total net periodic pension costs (income)	$ (10)	$ (2)	(34)	$ (7)
Walgreen profit sharing retirement trust
Defined Contribution Plan Disclosure [Line Items]
Profit sharing provision expense	58	53	183	164
Alliance Boots retirement savings plan
Defined Contribution Plan Disclosure [Line Items]
Cost recognized in the consolidated condensed statements of earnings	32	33	96	94
Selling, general and administrative expenses | Boots and other pension plans
Components of net periodic benefit costs [Abstract]
Service costs	2	2	4	5
Other income (expense) | Boots and other pension plans
Components of net periodic benefit costs [Abstract]
Interest costs	49	50	148	146
Expected returns on plan assets/other	$ (61)	$ (54)	$ (186)	$ (158)