Description of Business, Company History and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation. These accompanying unaudited interim Consolidated and Combined Financial Statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and the rules and regulations of the SEC for interim financial statements. Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to the rules and regulations of the SEC. These Consolidated and Combined Financial Statements should be read in conjunction with the audited Consolidated and Combined Financial Statements and the notes thereto for the year ended December 31, 2017, which are included in the Company's Annual Report on Form 10-K dated March 6, 2018 (the “December 31, 2017 Consolidated and Combined Financial Statements”). The significant accounting policies used in preparing these Consolidated and Combined Financial Statements were applied on a basis consistent with those reflected in the December 31, 2017 Consolidated and Combined Financial Statements. In the opinion of management, the Consolidated and Combined Financial Statements contain all adjustments (consisting of a normal, recurring nature) necessary to present fairly the Company's financial position, results of operations, cash flows and changes in stockholders' equity as of the dates and for the periods indicated. The unaudited results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of results that may be expected for the year ended December 31, 2018.
Use of Estimates	Use of Estimates. The preparation of the accompanying unaudited interim Consolidated and Combined Financial Statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect amounts reported in the Consolidated and Combined Financial Statements and accompanying disclosures. Although these estimates are based on management’s best knowledge of current events and actions that the Company may undertake in the future, actual results may differ from those estimates.
Principles of Consolidation	Principles of Consolidation. The accompanying unaudited Consolidated and Combined Financial Statements include the accounts of Cars.com Inc. and its 100% owned subsidiaries. All intercompany transactions and accounts are eliminated in consolidation. The accompanying unaudited Consolidated and Combined Financial Statements for the period prior to the Separation are derived from the historical accounting records of TEGNA and present its financial position, results of operations and cash flows as if the Company were a separate entity for the period prior to the Separation and include allocations of certain TEGNA corporate expenses, such as insurance and other general corporate overhead expenses. All significant intercompany transactions between either (i) the Company and TEGNA or (ii) the Company and TEGNA affiliates have been included within the Consolidated and Combined Financial Statements and are considered to be effectively settled through equity contributions or distributions at the time the transactions were recorded. The total net effect of these intercompany transactions is reflected in “Transactions with TEGNA, net” in the Consolidated and Combined Statements of Cash Flows as financing activities.
Reclassifications	Reclassifications. Certain prior year balances have been reclassified to conform to the current year presentation. Cost of revenues and operations have been reclassified from the product support, technology and operations line item into a separate line item. Depreciation expense amounts have also been reclassified from the General and administrative line item into the amortization of intangible assets line item, which has been renamed Depreciation and amortization. There are no changes to total Operating expenses, Operating income or Net income.
Recent Accounting Pronouncements	NOTE 2. Recent Accounting Pronouncements Revenue Recognition. The Financial Accounting Standards Board (the “FASB”) amended the FASB Accounting Standards Codification (“ASC”) and created Topic 606, Revenue from Contracts with Customers (“ASC 606”). Under ASC 606, revenue recognition occurs when a customer obtains control of promised goods or services in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. In addition, ASC 606 requires additional disclosures about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The Company’s primary source of revenue is the sale of online subscription advertising products and services, which will continue to be recognized ratably over the contract term as the service is provided to the customer. Effective January 1, 2018, the Company adopted ASC 606 using the modified retrospective method. The adoption did not have a material impact on its Consolidated and Combined Financial Statements. For further information, see Note 10 (Revenues). Financial Instruments – Equity Investments. In January 2016, the FASB issued Accounting Standards Update (“ASU”) No. 2016-01, Financial Instruments—Overall, amending several elements surrounding the recognition and measurement of financial instruments and requiring equity investments (except those accounted for under the equity method of accounting or those that result in consolidation) to be measured at fair value with changes in fair value recognized in net income. Effective January 1, 2018, the Company adopted this ASU on a prospective basis. The adoption did not have a material impact on its Consolidated and Combined Financial Statements and related disclosures. Financial Instruments – Credit Losses. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses changing the way credit losses on accounts receivable are estimated. Under current U.S. GAAP, credit losses on trade accounts receivable are recognized once it is probable that such losses will occur. Under this new guidance, the Company will be required to estimate credit losses based on the expected amount of future collections which may result in earlier recognition of allowance for doubtful accounts. The new guidance is effective for the Company on January 1, 2020 and will be adopted using a modified retrospective approach. The Company is currently evaluating this new guidance and does not expect it to have a material impact on its Consolidated and Combined Financial Statements and related disclosures. Stock-Based Compensation. In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation, clarifying when changes to the terms or conditions of a stock-based payment award must be accounted for as modifications and allowing for certain changes to awards without accounting for them as modifications. Effective January 1, 2018, the Company adopted the ASU on a prospective basis. The adoption did not have a material impact on its Consolidated and Combined Financial Statements and related disclosures. Definition of a Business. In January 2017, the FASB issued ASU 2017-01, Business Combinations, clarifying the definition of a business with the objective of adding guidance to assist companies with evaluating whether transactions should be accounted for as acquisitions or disposals of assets or businesses. Effective January 1, 2018, the Company adopted this ASU on a prospective basis. The adoption did not have a material impact on its Consolidated and Combined Financial Statements and related disclosures. Leases. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) requiring lessees to recognize assets and liabilities on the Consolidated and Combined Balance Sheets for leases with lease terms of more than 12 months and to disclose additional quantitative and qualitative information about leasing arrangements. The new guidance is effective for the Company on January 1, 2019. The Company plans to utilize the package of practical expedients and to initially apply Topic 842 as of January 1, 2019 and recognize a cumulative-effect adjustment to the opening balance of retained earnings. Although the Company is currently evaluating the provisions of the ASU to determine its full impact on the Company’s Consolidated and Combined Financial Statements, the primary impact will be to record assets and liabilities for current operating leases, which are principally related to real estate. Cloud Computing Arrangements. In August 2018, the FASB issued ASU 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, aligning the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs for internal-use software. The new guidance is effective for the Company on January 1, 2020 and early adoption is permitted. The Company is currently evaluating this new guidance and does not expect it to have a material impact on its Consolidated and Combined Financial Statements and related disclosures.