| Document and Entity Information | Apr. 28, 2022 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001745041 |
| Document Type | 8-K |
| Document Period End Date | Apr. 28, 2022 |
| Entity Registrant Name | IAA, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-38580 |
| Entity Tax Identification Number | 83-1030538 |
| Entity Address, Address Line One | Two Westbrook Corporate Center |
| Entity Address, Address Line Two | Suite 500 |
| Entity Address, City or Town | Westchester |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 60154 |
| City Area Code | (708) |
| Local Phone Number | 492-7000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | IAA |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
