Retirement benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2017	May 31, 2016
Components of net periodic benefit costs [Abstract]
Employer cash contributions to defined benefit pension plans			$ 48
Employee expected additional contribution in current fiscal year			18
Walgreen Profit Sharing Retirement Trust
Defined Contribution Plan Disclosure [Line Items]
Profit sharing provision expense	$ 58	$ 58	164	$ 169
Alliance Boots Retirement Savings Plan
Defined Contribution Plan Disclosure [Line Items]
Cost recognized in the consolidated condensed statements of earnings	26	33	82	102
Boots and Other Pension Plans
Components of net periodic benefit costs [Abstract]
Service costs	1	1	3	3
Interest costs	43	77	129	236
Expected returns on plan assets/other	(41)	(62)	(112)	(189)
Total net periodic pension costs	3	$ 16	$ 20	$ 50
Postretirement Health Coverage
Components of net periodic benefit costs [Abstract]
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments	$ 109