Acquisitions - summary of identified assets acquired and liabilities assumed (Details) - USD ($) $ in Millions		12 Months Ended
	Mar. 31, 2017	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Identifiable assets acquired and liabilities assumed
Goodwill		$ 16,560	$ 16,914	$ 15,632
Rite Aid
Business Acquisition [Line Items]
Total consideration		4,330	4,300
Identifiable assets acquired and liabilities assumed
Inventories		1,171
Property, plant and equipment		490
Intangible assets		2,039	$ 2,054
Accrued expenses and other liabilities		(55)
Deferred income taxes		291
Other non-current liabilities		(937)
Total identifiable net assets		2,999
Goodwill		$ 1,331
AllianceRx Walgreens Prime
Business Acquisition [Line Items]
Total consideration	$ 720
Identifiable assets acquired and liabilities assumed
Accounts receivable	217
Inventories	149
Property, plant and equipment	11
Intangible assets	331
Trade accounts payable	(90)
Accrued expenses and other liabilities	(1)
Total identifiable net assets	617
Goodwill	$ 103