Summary of major accounting policies - liabilities for store closings (Details) - USD ($) $ in Millions	Aug. 31, 2018	Aug. 31, 2017
Accounting Policies [Abstract]
Reserve for store closings	$ 964	$ 718

Liability as of the balance sheet date for facility closings and related lease termination charges. This liability is based on the present value of future rent obligations and other related costs (net of estimated sublease rent) to the first lease option date.

No definition available.

Name:	wba_FacilityClosingsAndRelatedLeaseTerminationChargesReserve
Namespace Prefix:	wba_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant