Basis of Presentation and Nature of Operations (Policies)	3 Months Ended
	Mar. 29, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	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 unaudited consolidated financial statements for the three months ended March 31, 2019 and condensed 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 unaudited consolidated financial statements. The Company's historical results of operations, financial position and cash flows presented in the unaudited 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 unaudited 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 2 - Relationship with KAR and Related Entities. The accompanying unaudited consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America ("U.S. GAAP") for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and notes required by U.S. GAAP for annual financial statements. Operating results for interim periods are not necessarily indicative of results that may be expected for the year as a whole. In the opinion of management, the unaudited consolidated financial statements reflect all adjustments, generally consisting of normal recurring accruals, necessary for a fair statement of our results of operations, cash flows and financial position for the periods presented. These unaudited consolidated financial statements and condensed notes thereto are unaudited and should be read in conjunction with the audited consolidated financial statements and notes thereto, for the year ended December 29, 2019 included in the Company's Annual Report on Form 10-K filed with the Securities and Exchange Commission (the "SEC") on March 18, 2020.
Use of Estimates	Use of Estimates The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates based in part on assumptions about current, and for some estimates, future economic and market conditions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the period. Although the current estimates contemplate current conditions and expected future changes, as appropriate, it is reasonably possible that future conditions could differ from these estimates, which could materially affect the Company's results of operations and financial position. Among other effects, such changes could result in future impairments of goodwill, intangible assets and long-lived assets, additional allowances on accounts receivable and deferred tax assets and changes in litigation and other loss contingencies.
Reclassification	Reclassification Certain amounts reported in the Company's Registration Statement on Form 10 filed with the SEC on June 13, 2019 have been reclassified to conform to the current year’s presentation. The reclassification is related to the presentation of outstanding checks of one of the Company's subsidiaries.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Issued and Adopted Accounting Pronouncements In August 2018, the FASB issued Accounting Standards Update ("ASU") 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract, which aligns the requirements for capitalizing implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The adoption of ASU 2018-15 on December 30, 2019 did not have a material impact on the Company's consolidated financial statements. In January 2017, the FASB issued ASU 2017-4, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, which simplifies the test for goodwill impairment by eliminating Step 2 (implied fair value measurement). Instead goodwill impairment would be measured as the amount by which a reporting unit's carrying amount exceeds its fair value, not to exceed the carrying amount of goodwill. The adoption of ASU 2017-4 on December 30, 2019 did not have a material impact on the Company's consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326), which updates the guidance related to the measurement of credit losses on financial instruments, including trade receivables. This ASU requires the recognition of credit losses on financial instruments based on an estimate of expected losses, replacing the incurred loss model in the prior guidance. The adoption of ASU 2016-13 on December 30, 2019 did not have a material impact on the Company's consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted The Company does not believe that any recently issued, but not yet effective, accounting pronouncements, if adopted, would have a material impact on its unaudited consolidated financial statements or disclosures.