Retirement benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2018	May 31, 2017
Components of net periodic benefit costs [Abstract]
Employer cash contributions to defined benefit pension plans			$ 57
Employee expected additional contribution in current fiscal year			7
Postretirement Health Plan
Components of net periodic benefit costs [Abstract]
Gain due to curtailment		$ 109
Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Service costs	$ 2	1	5	$ 3
Interest costs	50	43	146	129
Expected returns on plan assets/other	(54)	(41)	(158)	(112)
Total net periodic pension costs	(2)	3	(7)	20
Walgreen Profit Sharing Retirement Trust
Defined Contribution Plan Disclosure [Line Items]
Profit sharing provision expense	53	58	164	164
Alliance Boots Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Cost recognized in the consolidated condensed statements of earnings	$ 33	$ 26	$ 94	$ 82