Cover Page - USD ($) $ in Billions	12 Months Ended
	Aug. 31, 2021	Sep. 30, 2021	Feb. 28, 2021
Document Information [Line Items]
Document Type	10-K/A
Document Annual Report	true
Document Period End Date	Aug. 31, 2021
Current Fiscal Year End Date	--08-31
Document Transition Report	false
Entity File Number	001-36759
Entity Registrant Name	WALGREENS BOOTS ALLIANCE, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-1758322
Entity Address, Address Line One	108 Wilmot Road
Entity Address, City or Town	Deerfield
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60015
City Area Code	847
Local Phone Number	315-3700
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 34.3
Entity Common Stock, Shares Outstanding (in shares)		865,612,358
Documents Incorporated by Reference	Portions of the definitive proxy statement for our Annual Meeting of Stockholders planned to be held on January 27, 2022 are incorporated by reference into Part III of this Form 10-K as indicated herein.
Entity Central Index Key	0001618921
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	true
Amendment Description	WBA is filing this Amendment to amend Item 15 to include the consolidated financial statements of its equity investee, AmerisourceBergen Corporation (“ABC”) as of September 30, 2021
Common Stock, $0.01 par value
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	WBA
Security Exchange Name	NASDAQ
3.600% Walgreens Boots Alliance, Inc. notes due 2025
Document Information [Line Items]
Title of 12(b) Security	3.600% Walgreens Boots Alliance, Inc. notes due 2025
Trading Symbol	WBA25
Security Exchange Name	NASDAQ
2.125% Walgreens Boots Alliance, Inc. notes due 2026
Document Information [Line Items]
Title of 12(b) Security	2.125% Walgreens Boots Alliance, Inc. notes due 2026
Trading Symbol	WBA26
Security Exchange Name	NASDAQ