Interim Financial Statements (Policies)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	The accompanying Unaudited Condensed Consolidated Financial Statements include the accounts of AutoNation, Inc. and its subsidiaries; intercompany accounts and transactions have been eliminated. The accompanying Unaudited Condensed Consolidated Financial Statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and in accordance with the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. Additionally, operating results for interim periods are not necessarily indicative of the results that can be expected for a full year. The Unaudited Condensed Consolidated Financial Statements herein should be read in conjunction with our audited Consolidated Financial Statements and notes thereto included within our most recent Annual Report on Form 10-K. These Unaudited Condensed Consolidated Financial Statements reflect, in the opinion of management, all material adjustments (which include only normal recurring adjustments) necessary to fairly state, in all material respects, our financial position and results of operations for the periods presented.
Use of Estimates	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions 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 revenue and expenses during the reporting period. In preparing these financial statements, management has made its best estimates and judgments of certain amounts included in the financial statements. We base our estimates and judgments on historical experience and other assumptions that we believe are reasonable. However, application of these accounting policies involves the exercise of judgment and use of assumptions as to future uncertainties and, as a result, actual results could differ materially from these estimates. We periodically evaluate estimates and assumptions used in the preparation of the financial statements and make changes on a prospective basis when adjustments are necessary. Such estimates and assumptions affect, among other things, our goodwill, indefinite-lived intangible asset, and long-lived asset valuations; inventory valuation; equity investment valuation; assets held for sale; accruals for chargebacks against revenue recognized from the sale of finance and insurance products; accruals related to self-insurance programs; certain legal proceedings; assessment of the annual income tax expense; valuation of deferred income taxes and income tax contingencies; the allowance for expected credit losses; and measurement of performance-based compensation costs.
Earnings Per Share	Basic earnings per share (“EPS”) is computed by dividing net income by the weighted average number of common shares outstanding for the period, including vested restricted stock unit (“RSU”) awards. Diluted EPS is computed by dividing net income by the weighted average number of shares outstanding, noted above, adjusted for the dilutive effect of stock options and unvested RSU awards.
Impairment Of Long-Lived Assets	Nonfinancial assets such as goodwill, other intangible assets, long-lived assets held and used, and right-of-use assets are measured at fair value when there is an indicator of impairment and recorded at fair value only when impairment is recognized or for a business combination. The fair values less costs to sell of long-lived assets held for sale are assessed each reporting period they remain classified as held for sale. Subsequent changes in the held for sale long-lived asset’s fair value less cost to sell (increase or decrease) is reported as an adjustment to its carrying amount, except that the adjusted carrying amount cannot exceed the carrying amount of the long-lived asset at the time it was initially classified as held for sale.