Background Basis of Accounting (Policies)	9 Months Ended
Background Basis of Accounting (Policies)	Nov. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Background	Business. CarMax, Inc. (“we,” “our,” “us,” “CarMax” and “the company”), including its wholly owned subsidiaries, is the largest retailer of used vehicles in the United States. We operate in two reportable segments: CarMax Sales Operations and CarMax Auto Finance (“CAF”). Our CarMax Sales Operations segment consists of all aspects of our auto merchandising and service operations, excluding financing provided by CAF. Our CAF segment consists solely of our own finance operation that provides financing to customers buying retail vehicles from CarMax. We deliver an unrivaled customer experience by offering a broad selection of quality used vehicles and related products and services at competitive, no-haggle prices using a customer-friendly sales process in an attractive, modern sales facility, as well as through carmax.com and our mobile apps. We provide customers with a range of related products and services, including the appraisal and purchase of vehicles directly from consumers; the financing of retail vehicle purchases through CAF and third-party finance providers; the sale of extended protection plan (“EPP”) products, which include extended service plans (“ESPs”) and guaranteed asset protection (“GAP”); and vehicle repair service. Vehicles purchased through the appraisal process that do not meet our retail standards are sold to licensed dealers through on-site wholesale auctions.
Basis of Presentation	Basis of Presentation and Use of Estimates. The accompanying interim unaudited consolidated financial statements include the accounts of CarMax and our wholly owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the opinion of management, such interim consolidated financial statements reflect all normal recurring adjustments considered necessary to present fairly the financial position and the results of operations and cash flows for the interim periods presented. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the full fiscal year. The accounting policies followed in the presentation of our interim financial results are consistent with those included in the company’s Annual Report on Form 10-K for the fiscal year ended February 28, 2019 (the “2019 Annual Report”), with the exception of those related to recent accounting pronouncements adopted in the current fiscal year. These consolidated financial statements should be read in conjunction with the audited consolidated financial statements and footnotes included in our 2019 Annual Report.
Use of Estimates	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates. Certain prior year amounts have been reclassified to conform to the current year’s presentation. Amounts and percentages may not total due to rounding.
Recent Accounting Pronouncements	Recent Accounting Pronouncements. Effective in Future Periods. In June 2016, the Financial Accounting Standards Board (“FASB”) issued an accounting pronouncement (FASB ASU 2016-13) related to the measurement of credit losses on financial instruments. This pronouncement, along with subsequent ASUs issued to clarify certain provisions of ASU 2016-13, changes the impairment model for most financial assets and will require the use of an “expected loss” model for instruments measured at amortized cost. Under this model, entities will be required to estimate the lifetime expected credit loss on such instruments and record an allowance to offset the amortized cost basis of the financial asset, resulting in a net presentation of the amount expected to be collected on the financial asset. In developing the estimate for lifetime expected credit loss, entities must incorporate historical experience, current conditions, and reasonable and supportable forecasts. This pronouncement is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2019. We have designed an allowance for loan loss methodology to comply with these new requirements, which will be adopted for our fiscal year beginning March 1, 2020. Based on information as of November 30, 2019, we expect to record a $200-250 million increase in the allowance for loan losses on our opening consolidated balance sheet as of March 1, 2020, with a corresponding net-of-tax adjustment to retained earnings. The expected increase in the allowance for loan losses is primarily the result of extending the loan loss forecast period from 12 months to the entire lifetime of the loan portfolio. The final adoption impact may vary depending on the company’s portfolio at the adoption date, as well as macroeconomic conditions and forecasts at that time. We expect this new methodology could increase volatility in our quarterly provision for loan losses, as we will be estimating loan losses over a longer forecast period. We are finalizing testing of the effectiveness of our new allowance for loan loss methodology, as well as designing the relevant controls and governance structure. In December 2019, the FASB issued an accounting pronouncement (FASB ASU 2019-12) related to simplifying the accounting for income taxes. The pronouncement is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. We are currently in the process of evaluating the effects of this pronouncement on our consolidated financial statements, including potential early adoption.