Acquisitions - Narrative (Details) $ in Millions			3 Months Ended	9 Months Ended
	Sep. 19, 2017 USD ($) distribution_center store	Mar. 31, 2017 USD ($)	May 31, 2018 USD ($) store	May 31, 2018 USD ($) store	Aug. 31, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 17,089	$ 17,089	$ 15,632
Rite Aid Corporation
Business Acquisition [Line Items]
Number of stores expected to be acquired | store	1,932
Number of distribution centers expected to be acquired | distribution_center	3
Consideration to be transferred	$ 4,375
Number of locations acquired | store			390	1,932
Cash consideration				$ 4,157
Total consideration			$ 820	4,330
Goodwill			$ 1,361	$ 1,361
AllianceRx Walgreens Prime
Business Acquisition [Line Items]
Total consideration		$ 720
Goodwill		$ 103
Payer contracts | AllianceRx Walgreens Prime
Business Acquisition [Line Items]
Weighted-average useful life (in years)		15 years