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Goodwill and other intangible assets - additional information (Details) $ in Millions		3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Aug. 31, 2019 USD ($)	Aug. 31, 2019 USD ($)	Aug. 31, 2018 USD ($) store	Aug. 31, 2017 USD ($)
Goodwill [Line Items]
Goodwill		$ 16,560	$ 16,560	$ 16,914	$ 15,632
Indefinite lived intangible assets		7,110	7,110	7,629
Goodwill acquired during period			8	1,348
Amortization expense for intangible assets			552	$ 493	$ 385
Rite Aid
Goodwill [Line Items]
Goodwill, purchase accounting adjustments			(13)
Goodwill		1,331	1,331
Number of stores acquired \| store				1,932
Total consideration			4,330	$ 4,300
Goodwill acquired during period				1,344
Intangible assets		$ 2,039	$ 2,039	2,054
AllianceRx Walgreens Prime
Goodwill [Line Items]
Goodwill	$ 103
Total consideration	720
Intangible assets	$ 331
Minimum
Goodwill [Line Items]
Reporting unit fair value in excess of carrying amount (as a percent)		9.00%	9.00%
Maximum
Goodwill [Line Items]
Reporting unit fair value in excess of carrying amount (as a percent)		269.00%	269.00%
Pharmacy licenses
Goodwill [Line Items]
Indefinite lived intangible assets		$ 1,878	$ 1,878	$ 2,072
Boots Reporting Unit
Goodwill [Line Items]
Goodwill		2,600	2,600
Indefinite lived intangible assets		$ 6,900	$ 6,900
Boots Reporting Unit \| Trade names \| Minimum
Goodwill [Line Items]
Reporting unit fair value in excess of carrying amount (as a percent)		3.00%	3.00%
Boots Reporting Unit \| Trade names \| Maximum
Goodwill [Line Items]
Reporting unit fair value in excess of carrying amount (as a percent)		29.00%	29.00%
Boots Reporting Unit \| Pharmacy licenses
Goodwill [Line Items]
Impairment of intangible assets		$ 73
Retail Pharmacy International \| Boots Reporting Unit
Goodwill [Line Items]
Reporting unit fair value in excess of carrying amount (as a percent)		9.00%	9.00%