Cover Page - USD ($)	12 Months Ended
	Jan. 01, 2023	Feb. 14, 2023	Jul. 01, 2022
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Jan. 01, 2023
Current Fiscal Year End Date	--01-01
Document Transition Report	false
Entity File Number	001-38580
Entity Registrant Name	IAA, Inc.
Entity Incorporation, State or Country Code	DE
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
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	IAA
Security Exchange Name	NYSE
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			$ 4,426,719,223
Entity Common Stock, Shares Outstanding		133,858,743
Documents Incorporated by Reference	Not Applicable
Entity Central Index Key	0001745041
Amendment Flag	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY