Basis of Presentation	12 Months Ended
Dec. 29, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Description of Business IAA, Inc., together with its subsidiaries (collectively referred to herein as "IAA" and "the Company") is a leading provider of auction solutions for total loss, damaged and low-value vehicles in North America and the United Kingdom. The Company facilitates the marketing and sale of total loss, damaged and low-value vehicles for a full spectrum of sellers. The Company’s solutions, which are focused on a diverse set of global customers, provide buyers with the vehicles they need to, among other things, fulfill their vehicle rebuild requirements, replacement part inventory or scrap demand. The Company operates in two reportable segments: United States and International. Separation and Distribution On February 27, 2018, KAR Auction Services, Inc. (“KAR” or “Former Parent”), a Delaware corporation, announced a plan to pursue the separation and spin-off (the “Separation”) of its salvage auction business into a separate public company, IAA Spinco Inc. IAA Spinco Inc. was incorporated in Delaware on June 19, 2018 and was renamed IAA, Inc. on June 27, 2019. On June 28, 2019 (the "Separation Date"), KAR completed the distribution of 100% of the issued and outstanding shares of common stock of IAA to the holders of record of KAR's common stock on June 18, 2019, on a pro rata basis (the "Distribution"). On the Separation Date, each KAR common stockholder of record received one share of IAA common stock for every one share of KAR common stock held by such stockholder as of the record date. As a result of the Distribution, KAR does not retain any ownership interest in IAA. The Distribution was made pursuant to the Separation and Distribution Agreement, dated June 27, 2019 (the "Separation and Distribution Agreement"), pursuant to which KAR contributed the subsidiaries that operated the salvage auction business to IAA. The Distribution is expected to be a tax-free transaction under provisions of the Internal Revenue Code. Following the Distribution, IAA became an independent publicly-traded company and is listed on the New York Stock Exchange under the symbol “IAA.” In connection with the Separation, on the Separation Date, the Company paid a dividend to KAR of $1,278.0 million, which included $456.6 million to settle intercompany debt and $40.9 million for certain fixed assets transferred to the Company by KAR on the Separation Date. The Company also paid KAR $117.8 million on the Separation Date to settle other intercompany accounts in connection with the Separation. In connection with the Separation, the Company also entered into a non-compete and various other ancillary agreements to effect the Separation and provide a framework for the Company's relationship with KAR after the Separation, including a transition services agreement, a tax matters agreement and an employee matters agreement. These agreements provide for the allocation of assets, employees, liabilities and obligations attributable to periods prior to, at and after the Company’s Separation from KAR and govern certain relationships between the Company and KAR after the Separation. For further information regarding these agreements, see Note 3 - Relationship with KAR and Related Entities. Basis of Presentation Until the Separation Date, the Company operated as a separate reportable segment within KAR and, since the Separation Date, the Company has operated independently from KAR. The accompanying consolidated financial statements as of December 30, 2018, for the fiscal years ended December 30, 2018, and for the period from December 31, 2018, to the Separation Date, and notes related thereto have been prepared from KAR’s historical accounting records and are presented on a stand-alone basis as if IAA's operations had been conducted independently from KAR for all periods prior to the Separation Date. Accordingly, prior to the Separation Date, KAR’s net investment in these operations (Net Parent Investment) was shown in lieu of stockholder’s (deficit) equity in the consolidated financial statements. The Company’s historical results of operations, financial position and cash flows presented in the consolidated financial statements may not be indicative of what they would have been had the Company actually been a separate stand-alone entity during such periods, nor are they necessarily indicative of the Company's future results of operations, financial position and cash flows. IAA is comprised of certain stand-alone legal entities for which discrete financial information is available. The consolidated statements of income include all revenues and costs directly attributable to IAA, including costs for functions and services used by the Company. Prior to the Separation Date, certain shared costs were directly charged to the Company by KAR based on specific identification or other allocation methods. The Company’s results of operations prior to the Separation Date also include allocations of costs for administrative functions and services performed on behalf of the Company by centralized staff groups within KAR. Current and deferred income taxes and related tax expense have been determined based on the Company's stand-alone results by applying Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 740, Income Taxes, to the Company’s operations in each country as if the Company was a separate taxpayer (i.e., following the separate return methodology). Allocation methodologies were applied to certain shared costs to allocate amounts to the Company as discussed further in Note 3 - Relationship with KAR and Related Entities.

Basis of Presentation

Description of Business

IAA, Inc., together with its subsidiaries (collectively referred to herein as "IAA" and "the Company") is a leading provider of auction solutions for total loss, damaged and low-value vehicles in North America and the United Kingdom. The Company facilitates the marketing and sale of total loss, damaged and low-value vehicles for a full spectrum of sellers. The Company’s solutions, which are focused on a diverse set of global customers, provide buyers with the vehicles they need to, among other things, fulfill their vehicle rebuild requirements, replacement part inventory or scrap demand. The Company operates in two reportable segments: United States and International.

Separation and Distribution

On February 27, 2018, KAR Auction Services, Inc. (“KAR” or “Former Parent”), a Delaware corporation, announced a plan to pursue the separation and spin-off (the “Separation”) of its salvage auction business into a separate public company, IAA Spinco Inc. IAA Spinco Inc. was incorporated in Delaware on June 19, 2018 and was renamed IAA, Inc. on June 27, 2019. On June 28, 2019 (the "Separation Date"), KAR completed the distribution of 100% of the issued and outstanding shares of common stock of IAA to the holders of record of KAR's common stock on June 18, 2019, on a pro rata basis (the "Distribution"). On the Separation Date, each KAR common stockholder of record received one share of IAA common stock for every one share of KAR common stock held by such stockholder as of the record date. As a result of the Distribution, KAR does not retain any ownership interest in IAA. The Distribution was made pursuant to the Separation and Distribution Agreement, dated June 27, 2019 (the "Separation and Distribution Agreement"), pursuant to which KAR contributed the subsidiaries that operated the salvage auction business to IAA. The Distribution is expected to be a tax-free transaction under provisions of the Internal Revenue Code. Following the Distribution, IAA became an independent publicly-traded company and is listed on the New York Stock Exchange under the symbol “IAA.”

In connection with the Separation, on the Separation Date, the Company paid a dividend to KAR of $1,278.0 million, which included $456.6 million to settle intercompany debt and $40.9 million for certain fixed assets transferred to the Company by KAR on the Separation Date. The Company also paid KAR $117.8 million on the Separation Date to settle other intercompany accounts in connection with the Separation.

In connection with the Separation, the Company also entered into a non-compete and various other ancillary agreements to effect the Separation and provide a framework for the Company's relationship with KAR after the Separation, including a transition services agreement, a tax matters agreement and an employee matters agreement. These agreements provide for the allocation of assets, employees, liabilities and obligations attributable to periods prior to, at and after the Company’s Separation from KAR and govern certain relationships between the Company and KAR after the Separation. For further information regarding these agreements, see Note 3 - Relationship with KAR and Related Entities.

Basis of Presentation

Until the Separation Date, the Company operated as a separate reportable segment within KAR and, since the Separation Date, the Company has operated independently from KAR. The accompanying consolidated financial statements as of December 30, 2018, for the fiscal years ended December 30, 2018, and for the period from December 31, 2018, to the Separation Date, and notes related thereto have been prepared from KAR’s historical accounting records and are presented on a stand-alone basis as if IAA's operations had been conducted independently from KAR for all periods prior to the Separation Date. Accordingly, prior to the Separation Date, KAR’s net investment in these operations (Net Parent Investment) was shown in lieu of stockholder’s (deficit) equity in the consolidated financial statements. The Company’s historical results of operations, financial position and cash flows presented in the consolidated financial statements may not be indicative of what they would have been had the Company actually been a separate stand-alone entity during such periods, nor are they necessarily indicative of the Company's future results of operations, financial position and cash flows.

IAA is comprised of certain stand-alone legal entities for which discrete financial information is available. The consolidated statements of income include all revenues and costs directly attributable to IAA, including costs for functions and services used by the Company. Prior to the Separation Date, certain shared costs were directly charged to the Company by KAR based on specific identification or other allocation methods. The Company’s results of operations prior to the Separation Date also include allocations of costs for administrative functions and services performed on behalf of the Company by centralized staff groups within KAR. Current and deferred income taxes and related tax expense have been determined based on the Company's stand-alone results by applying Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 740, Income Taxes, to the Company’s operations in each country as if the Company was a separate taxpayer (i.e., following the separate return methodology). Allocation methodologies were applied to certain shared costs to allocate amounts to the Company as discussed further in Note 3 - Relationship with KAR and Related Entities.