| Pay vs Performance Disclosure - USD ($) | 12 Months Ended |
| Feb. 28, 2023 | Feb. 28, 2022 | Feb. 28, 2021 |
| Pay vs Performance Disclosure [Table] | | | |
| Pay vs Performance [Table Text Block] | PAY VERSUS PERFORMANCE TABLE Fiscal Year Summary Compensation Table Total for PEO (a) ($) Compensation Actually Paid to PEO (a) (b) (c) ($) Average Summary Compensation Table Total for Non-PEO NEOs (a) ($) Average Compensation Actually Paid to Non-PEO NEOs (a) (b) (c) ($) Value of Initial Fixed $100 Investment Based on: (d) Net Income Adjusted EBIT (e) ($ Millions) Total Shareholder Return Peer Group Total Shareholder Return 2023 11,588,743 (3,838,775) 2,374,371 (266,923) 79.07 124.47 485 749 2022 13,689,123 11,139,628 3,183,175 3,297,303 125.22 158.40 1,151 1,584 2021 9,891,893 31,282,047 3,057,748 8,306,849 136.88 147.99 747 1,050 | | |
| Named Executive Officers, Footnote [Text Block] | (a) Mr. Nash was our PEO for each fiscal year presented. The individuals comprising the Non-PEO NEOs for each year presented are listed below. Fiscal 2021 Fiscal 2022 Fiscal 2023 Enrique N. Mayor-Mora Enrique N. Mayor-Mora Enrique N. Mayor-Mora Edwin J. Hill James Lyski James Lyski Eric M. Margolin Shamim Mohammad Shamim Mohammad Thomas W. Reedy Diane L. Cafritz Diane L. Cafritz Edwin J. Hill Eric M. Margolin | | |
| Peer Group Issuers, Footnote [Text Block] | The Peer Group TSR set forth in this table utilizes the S&P 500 Retailing Index, which we also utilize in the stock performance graph required by Item 201(e) of Regulation S-K included in our Annual Report for the year ended February 28, 2023. The comparison assumes $100 was invested for the period starting February 29, 2020, through the end of the listed year in the Company and in the S&P 500 Retailing Index, respectively. Historical stock performance is not necessarily indicative of future stock performance. | | |
| PEO Total Compensation Amount | $ 11,588,743 | $ 13,689,123 | $ 9,891,893 |
| PEO Actually Paid Compensation Amount | $ (3,838,775) | 11,139,628 | 31,282,047 |
| Adjustment To PEO Compensation, Footnote [Text Block] | Compensation Actually Paid reflects the exclusions and inclusions of certain amounts for the PEO and the Non-PEO NEOs as set forth below. Equity values are calculated in accordance with FASB ASC Topic 718. Amounts in the Exclusion of Stock Awards and Option Awards column are the totals (or, in the case of the Non-PEO NEOs, the average of the totals) from the Stock Awards and Option Awards columns set forth in the Summary Compensation Table. Amounts in the Exclusion of Change in Pension Value column reflect the amounts attributable to the Change in Pension Value reported in the Summary Compensation Table. There were no adjustments for inclusion of pension service cost or prior service cost because the Company’s defined benefit pension plans were frozen as of December 31, 2008, as described in the narrative to the “Pension Benefits in Fiscal 2023” table. Year Summary Compensation Table Total for William D. Nash ($) Exclusion of Change in Pension Value for William D. Nash ($) Exclusion of Stock Awards and Option Awards for William D. Nash ($) Inclusion of Equity Values for William D. Nash ($) Compensation Actually Paid to William D. Nash ($) 2023 11,588,743 — (8,865,651) (6,561,867) (3,838,775) 2022 13,689,123 — (8,644,791) 6,095,296 11,139,628 2021 9,891,893 (977) (6,999,999) 28,391,130 31,282,047 Fiscal Year Average Summary Compensation Table Total for Non-PEO NEOs ($) Average Exclusion of Change in Pension Value for Non-PEO NEOs Average Exclusion of Stock Awards and Option Awards for Non-PEO NEOs Average Inclusion of Equity Values for Non-PEO NEOs ($) Average Compensation Actually Paid to Non-PEO NEOs ($) 2023 2,374,371 — (1,361,434) (1,279,860) (266,923) 2022 3,183,175 (692) (1,697,356) 1,812,176 3,297,303 2021 3,057,748 (4,870) (1,830,920) 7,084,891 8,306,849 The amounts in the Inclusion of Equity Values in the tables above are derived from the amounts set forth in the following tables: Fiscal Year Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested as of Last Day of Year for William D. Nash ($) Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards Granted in a Prior Year for William D. Nash ($) Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year for William D. Nash ($) Change in Fair Value from Last Day of Prior Year to Vesting Date of Equity Awards Granted in a Prior Year that Vested During Year for William D. Nash ($) Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year for William D. Nash ($) Total - Inclusion of Equity Values for William D. Nash ($) 2023 6,188,670 (8,972,961) — (3,777,576) — (6,561,867) 2022 6,285,491 (3,529,135) — 3,338,940 — 6,095,296 2021 17,423,079 12,751,653 — (1,783,602) — 28,391,130 Fiscal Year Average Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested as of Last Day of Year for Non-PEO NEOs Average Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards Granted in a Prior Year for Non-PEO NEOs Average Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year for Non-PEO NEOs ($) Average Change in Fair Value from Last Day of Prior Year to Vesting Date of Equity Awards Granted in a Prior Year that Vested During Year for Non-PEO NEOs Average Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year for Non-PEO NEOs ($) Total - Average Inclusion of Equity Values for Non-PEO NEOs ($) 2023 950,489 (1,549,074) — (681,275) — (1,279,860) 2022 895,895 (458,627) 383,234 991,674 — 1,812,176 2021 3,486,985 2,438,705 1,016,899 142,302 — 7,084,891 | | |
| Non-PEO NEO Average Total Compensation Amount | $ 2,374,371 | 3,183,175 | 3,057,748 |
| Non-PEO NEO Average Compensation Actually Paid Amount | $ (266,923) | 3,297,303 | 8,306,849 |
| Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | Compensation Actually Paid reflects the exclusions and inclusions of certain amounts for the PEO and the Non-PEO NEOs as set forth below. Equity values are calculated in accordance with FASB ASC Topic 718. Amounts in the Exclusion of Stock Awards and Option Awards column are the totals (or, in the case of the Non-PEO NEOs, the average of the totals) from the Stock Awards and Option Awards columns set forth in the Summary Compensation Table. Amounts in the Exclusion of Change in Pension Value column reflect the amounts attributable to the Change in Pension Value reported in the Summary Compensation Table. There were no adjustments for inclusion of pension service cost or prior service cost because the Company’s defined benefit pension plans were frozen as of December 31, 2008, as described in the narrative to the “Pension Benefits in Fiscal 2023” table. Year Summary Compensation Table Total for William D. Nash ($) Exclusion of Change in Pension Value for William D. Nash ($) Exclusion of Stock Awards and Option Awards for William D. Nash ($) Inclusion of Equity Values for William D. Nash ($) Compensation Actually Paid to William D. Nash ($) 2023 11,588,743 — (8,865,651) (6,561,867) (3,838,775) 2022 13,689,123 — (8,644,791) 6,095,296 11,139,628 2021 9,891,893 (977) (6,999,999) 28,391,130 31,282,047 Fiscal Year Average Summary Compensation Table Total for Non-PEO NEOs ($) Average Exclusion of Change in Pension Value for Non-PEO NEOs Average Exclusion of Stock Awards and Option Awards for Non-PEO NEOs Average Inclusion of Equity Values for Non-PEO NEOs ($) Average Compensation Actually Paid to Non-PEO NEOs ($) 2023 2,374,371 — (1,361,434) (1,279,860) (266,923) 2022 3,183,175 (692) (1,697,356) 1,812,176 3,297,303 2021 3,057,748 (4,870) (1,830,920) 7,084,891 8,306,849 The amounts in the Inclusion of Equity Values in the tables above are derived from the amounts set forth in the following tables: Fiscal Year Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested as of Last Day of Year for William D. Nash ($) Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards Granted in a Prior Year for William D. Nash ($) Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year for William D. Nash ($) Change in Fair Value from Last Day of Prior Year to Vesting Date of Equity Awards Granted in a Prior Year that Vested During Year for William D. Nash ($) Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year for William D. Nash ($) Total - Inclusion of Equity Values for William D. Nash ($) 2023 6,188,670 (8,972,961) — (3,777,576) — (6,561,867) 2022 6,285,491 (3,529,135) — 3,338,940 — 6,095,296 2021 17,423,079 12,751,653 — (1,783,602) — 28,391,130 Fiscal Year Average Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested as of Last Day of Year for Non-PEO NEOs Average Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards Granted in a Prior Year for Non-PEO NEOs Average Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year for Non-PEO NEOs ($) Average Change in Fair Value from Last Day of Prior Year to Vesting Date of Equity Awards Granted in a Prior Year that Vested During Year for Non-PEO NEOs Average Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year for Non-PEO NEOs ($) Total - Average Inclusion of Equity Values for Non-PEO NEOs ($) 2023 950,489 (1,549,074) — (681,275) — (1,279,860) 2022 895,895 (458,627) 383,234 991,674 — 1,812,176 2021 3,486,985 2,438,705 1,016,899 142,302 — 7,084,891 | | |
| Compensation Actually Paid vs. Total Shareholder Return [Text Block] | Description of Relationship Between PEO and Non-PEO NEO Compensation Actually Paid and Total Shareholder Return (“TSR”) The following chart sets forth the relationship between (i) the Company’s cumulative TSR over the three most recently completed fiscal years and the S&P 500 Retailing Index’s cumulative TSR over the same period, and (ii) the Compensation Actually Paid to our PEO and the average of Compensation Actually Paid to our Non-PEO NEOs. | | |
| Compensation Actually Paid vs. Net Income [Text Block] | Description of Relationship Between PEO and Non-PEO NEO Compensation Actually Paid and Net Income The following chart sets forth the relationship between Compensation Actually Paid to our PEO, the average of Compensation Actually Paid to our Non-PEO NEOs, and our Net Income during the three most recently completed fiscal years. | | |
| Tabular List [Table Text Block] | CarMax used only the two financial performance measures set forth below to link Compensation Actually Paid to our NEOs for fiscal 2023 to company performance. Most Important Measures for Determining PEO and Non-PEO NEO Pay Adjusted EBIT Pre-tax Earnings Per Share | | |
| Total Shareholder Return Amount | $ 79.07 | 125.22 | 136.88 |
| Peer Group Total Shareholder Return Amount | 124.47 | 158.40 | 147.99 |
| Net Income (Loss) | $ 485 | $ 1,151,000 | $ 747,000 |
| Company Selected Measure Amount | 749 | 1,584 | 1,050 |
| Additional 402(v) Disclosure [Text Block] | The amounts shown for Compensation Actually Paid have been calculated in accordance with Item 402(v) of Regulation S-K and do not reflect compensation actually earned, realized, or received by the Company’s NEOs. These amounts reflect the Summary Compensation Table Total with certain adjustments as described in footnote (c) below. | | |
| Compensation Actually Paid vs. Adjusted EBIT | Description of Relationship Between PEO and Non-PEO NEO Compensation Actually Paid and Company-Selected Measure The following chart sets forth the relationship between Compensation Actually Paid to our PEO, the average of Compensation Actually Paid to our Non-PEO NEOs, and our Adjusted EBIT during the three most recently completed fiscal years. | | |
| Measure [Axis]: 1 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | Adjusted EBIT | | |
| Non-GAAP Measure Description [Text Block] | We determined Adjusted EBIT to be the most important financial performance measure used to link Company performance to Compensation Actually Paid to our PEO and Non-PEO NEOs for our fiscal year ended February 28, 2023. EBIT is earnings before interest and taxes, and the Committee defined “Adjusted EBIT” as EBIT that excludes the impact of any unrealized gains or losses on equity investments in private companies (or companies in which CarMax initially invested while that company was private but had subsequently gone public); however, including in EBIT for the relevant fiscal year the realized gains and losses in those investments to the extent that such gains or losses were realized in the applicable fiscal year. Adjusted EBIT may not have been the most important financial performance measure for fiscal years 2022 and 2021 and we may determine a different financial performance measure to be the most important financial performance measure in future years. | | |
| Measure [Axis]: 2 | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Measure Name | Pre-tax Earnings Per Share | | |
| PEO [Member] | Exclusion of Change in Pension Value [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | $ 0 | $ 0 | $ (977) |
| PEO [Member] | Exclusion of Stock Awards and Option Awards [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (8,865,651) | (8,644,791) | (6,999,999) |
| PEO [Member] | Inclusion of Equity Values [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (6,561,867) | 6,095,296 | 28,391,130 |
| PEO [Member] | Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested as of Last Day of Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 6,188,670 | 6,285,491 | 17,423,079 |
| PEO [Member] | Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards Granted in a Prior Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (8,972,961) | (3,529,135) | 12,751,653 |
| PEO [Member] | Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 0 | 0 | 0 |
| PEO [Member] | Change in Fair Value from Last Day of Prior Year to Vesting Date of Equity Awards Granted in a Prior Year that Vested During Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (3,777,576) | 3,338,940 | (1,783,602) |
| PEO [Member] | Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 0 | 0 | 0 |
| Non-PEO NEO [Member] | Exclusion of Change in Pension Value [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 0 | (692) | (4,870) |
| Non-PEO NEO [Member] | Exclusion of Stock Awards and Option Awards [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (1,361,434) | (1,697,356) | (1,830,920) |
| Non-PEO NEO [Member] | Inclusion of Equity Values [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (1,279,860) | 1,812,176 | 7,084,891 |
| Non-PEO NEO [Member] | Average Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested as of Last Day of Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 950,489 | 895,895 | 3,486,985 |
| Non-PEO NEO [Member] | Average Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards Granted in a Prior Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (1,549,074) | (458,627) | 2,438,705 |
| Non-PEO NEO [Member] | Average Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 0 | 383,234 | 1,016,899 |
| Non-PEO NEO [Member] | Average Change in Fair Value from Last Day of Prior Year to Vesting Date of Equity Awards Granted in a Prior Year that Vested During Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | (681,275) | 991,674 | 142,302 |
| Non-PEO NEO [Member] | Average Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | 0 | 0 | 0 |
| Non-PEO NEO [Member] | Total Average Inclusion of Equity Values [Member] | | | |
| Pay vs Performance Disclosure [Table] | | | |
| Adjustment to Compensation Amount | $ (1,279,860) | $ 1,812,176 | $ 7,084,891 |
