| Document and Entity Information | Oct. 15, 2020 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001618921 |
| Document Type | 8-K |
| Document Period End Date | Oct. 15, 2020 |
| Entity Registrant Name | WALGREENS BOOTS ALLIANCE, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36759 |
| 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 | 315-2500 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, $0.01 par value |
| Trading Symbol | WBA |
| Security Exchange Name | NASDAQ |
| M 2.875 Walgreens Boots Alliance Inc . Notes Due 2020 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.875% Walgreens Boots Alliance, Inc. notes due 2020 |
| Trading Symbol | WBA20 |
| Security Exchange Name | NASDAQ |
| M 3.600 Walgreens Boots Alliance Inc . Notes Due 2025 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 3.600% Walgreens Boots Alliance, Inc. notes due 2025 |
| Trading Symbol | WBA25 |
| Security Exchange Name | NASDAQ |
| M 2.125 Walgreens Boots Alliance Inc . Notes Due 2026 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.125% Walgreens Boots Alliance, Inc. notes due 2026 |
| Trading Symbol | WBA26 |
| Security Exchange Name | NASDAQ |
