| Document and Entity Information | Mar. 10, 2021 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001564406 |
| Document Type | 8-K |
| Document Period End Date | Mar. 10, 2021 |
| Entity Registrant Name | OAK STREET HEALTH, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 333-239818 |
| Entity Tax Identification Number | 84-3446686 |
| Entity Address, Address Line One | 30 W. Monroe Street |
| Entity Address, Address Line Two | Suite 1200 |
| Entity Address, City or Town | Chicago |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60603 |
| City Area Code | (312) |
| Local Phone Number | 733-9730 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.001 par value |
| Trading Symbol | OSH |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
