| Form N-CSR Cover | 6 Months Ended |
| Dec. 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | BRUCE FUND INC |
| Entity Central Index Key | 0000047071 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Dec. 31, 2024 |
| Shareholder Report | 6 Months Ended |
| Dec. 31, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | BRUCE FUND INC |
| Entity Central Index Key | 0000047071 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Dec. 31, 2024 |
| C000031584 | |
| Shareholder Report [Line Items] | |
| Fund Name | Bruce Fund |
| Trading Symbol | BRUFX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about Bruce Fund for the period of July 1, 2024 to December 31, 2024. |
| Shareholder Report Annual or Semi-Annual | Semi-Annual Shareholder Report |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.thebrucefund.com/document-library |
| Material Fund Change Notice [Text Block] | This report describes changes to the Fund that occurred during the reporting period. |
| Additional Information Phone Number | (800) 872-7823 |
| Additional Information Website | https://www.thebrucefund.com/document-library |
| Expenses [Text Block] | What were the Fund’s costs for the last six months? (based on a hypothetical $10,000 investment) Fund Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Bruce Fund $33 0.65% |
| Expenses Paid, Amount | $ 33 |
| Expense Ratio, Percent | 0.65% |
| Performance Past Does Not Indicate Future [Text] | The Fund's past performance is not a good predictor of how the Fund will perform in the future. |
| Line Graph [Table Text Block] | Bruce Fund S&P 500 ® Dec-2014 $10,000 $10,000 Dec-2015 $10,290 $10,138 Dec-2016 $10,708 $11,351 Dec-2017 $12,042 $13,829 Dec-2018 $11,565 $13,223 Dec-2019 $14,158 $17,386 Dec-2020 $15,857 $20,585 Dec-2021 $18,617 $26,494 Dec-2022 $16,986 $21,696 Dec-2023 $16,859 $27,399 Dec-2024 $17,628 $34,254 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 1 Year 5 Years 10 Years Bruce Fund 4.56% 4.48% 5.83% S&P 500 ® 25.02% 14.53% 13.10% The Fund's past performance is not a good predictor of how the Fund will perform in the future. The graph and table do not reflect the deduction of taxes that a shareholder would pay on fund distributions or redemption of fund shares. |
| No Deduction of Taxes [Text Block] | The graph and table do not reflect the deduction of taxes that a shareholder would pay on fund distributions or redemption of fund shares. |
| AssetsNet | $ 365,175,505 |
| Holdings Count | Holding | 42 |
| Advisory Fees Paid, Amount | $ 986,005 |
| InvestmentCompanyPortfolioTurnover | 8% |
| Additional Fund Statistics [Text Block] | Fund Statistics Net Assets $365,175,505 Number of Portfolio Holdings 42 Advisory Fee $986,005 Portfolio Turnover 8% |
| Holdings [Text Block] | Asset Weighting (% of total investments) Value Value Common Stocks 77.1% Convertible Bonds 0.4% Money Market Funds 18.8% U.S. Government & Agencies 3.7% |
| Material Fund Change [Text Block] | Material Fund Changes Effective October 28, 2024, as approved by the Board, the Adviser changed the annual percentage fee by decreasing the breakpoint for assets over $100,000,000 from 0.50% to 0.30%. |
| Shareholder Report, Line Graph (Details) - USD ($) | 6 Months Ended | ||||||||||
| Dec. 31, 2014 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | |
| C000031584 | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Bruce Fund | ||||||||||
| Account Value | $ 10,000 | $ 17,628 | $ 16,859 | $ 16,986 | $ 18,617 | $ 15,857 | $ 14,158 | $ 11,565 | $ 12,042 | $ 10,708 | $ 10,290 |
| S&P 500 Index | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | ®</sup> Index" id="sjs-B9">S&P 500<sup style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 700; grid-area: auto; line-height: 0px; margin: 0px; overflow: visible; position: relative; text-align: center;">®</sup> Index | ||||||||||
| Account Value | $ 10,000 | $ 34,254 | $ 27,399 | $ 21,696 | $ 26,494 | $ 20,585 | $ 17,386 | $ 13,223 | $ 13,829 | $ 11,351 | $ 10,138 |
| Shareholder Report, Average Annual Return (Details) | 6 Months Ended | 12 Months Ended | 60 Months Ended | 120 Months Ended |
| Dec. 31, 2014 | Dec. 31, 2024 | Dec. 31, 2024 | Dec. 31, 2024 | |
| C000031584 | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | Bruce Fund | |||
| Without Sales Load [Member] | C000031584 | ||||
| Average Annual Return [Line Items] | ||||
| Average Annual Return, Percent | 4.56% | 4.48% | 5.83% | |
| S&P 500 Index | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | ®</sup> Index" id="sjs-B11">S&P 500<sup style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 700; grid-area: auto; line-height: 0px; margin: 0px; overflow: visible; position: relative; text-align: center;">®</sup> Index | |||
| Average Annual Return, Percent | 25.02% | 14.53% | 13.10% |
| Shareholder Report, Holdings (Details) - C000031584 | Dec. 31, 2024 |
| 61747C707 | Morgan Stanley Institutional Liquidity Government Portfolio, Institutional Class | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.80% |
| 023586506 | U-Haul Holding Co., Class B | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7% |
| 020002101 | Allstate Corp. (The) | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.10% |
| 26441C204 | Duke Energy Corp. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.60% |
| 58933Y105 | Merck & Co., Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.50% |
| 00287Y109 | AbbVie, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.30% |
| 65339F101 | NextEra Energy, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.30% |
| 125896100 | CMS Energy Corp. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.10% |
| 002824100 | Abbott Laboratories | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.50% |
| 00206R102 | AT&T, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.40% |
| Materials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.30% |
| Technology | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| U.S. Treasury Obligations | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.80% |
| Consumer Staples | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| Communications | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| Financials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10% |
| Industrials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.90% |
| Money Market Funds | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.80% |
| Utilities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21.50% |
| Health Care | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 21.80% |
| InvestmentType_Common Stocks | |
| Holdings [Line Items] | |
| Percent of Total Investments | 77.10% |
| InvestmentType_Convertible Bonds | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.40% |
| InvestmentType_Money Market Funds | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.80% |
| InvestmentType_U.S. Government & Agencies | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
