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Goodwill and other intangible assets - additional information (Details) $ in Millions		12 Months Ended
	Sep. 19, 2017 USD ($)	Aug. 31, 2018 USD ($) store	Aug. 31, 2017 USD ($)	Aug. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)
Goodwill [Line Items]
Goodwill		$ 16,914	$ 15,632	$ 15,527
Amortization expense for intangible assets		$ 493	$ 385	$ 396
Rite Aid
Goodwill [Line Items]
Number of stores acquired \| store		1,932
Consideration	$ 4,330	$ 4,157
Goodwill	1,344
Intangible assets	$ 2,054
AllianceRx Walgreens Prime
Goodwill [Line Items]
Goodwill					$ 103
Intangible assets					$ 331
Minimum
Goodwill [Line Items]
Reporting unit fair value in excess of carrying amount (as a percent)		11.00%
Maximum
Goodwill [Line Items]
Reporting unit fair value in excess of carrying amount (as a percent)		312.00%