| Form N-CSR Cover | 12 Months Ended |
| Jun. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | BRUCE FUND INC |
| Entity Central Index Key | 0000047071 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Shareholder Report | 12 Months Ended |
| Jun. 30, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | BRUCE FUND INC |
| Entity Central Index Key | 0000047071 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| C000031584 | |
| Shareholder Report [Line Items] | |
| Fund Name | Bruce Fund |
| Trading Symbol | BRUFX |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Bruce Fund for the period of July 1, 2023 to June 30, 2024. |
| Additional Information [Text Block] | You can find additional information about the Fund at https://www.thebrucefund.com/document-library. You can also request this information by contacting us at (800) 872-7823. |
| 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 year? (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 $69 0.69% |
| Expenses Paid, Amount | $ 69 |
| Expense Ratio, Percent | 0.69% |
| 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 ® Jun-2014 $10,000 $10,000 Jun-2015 $9,887 $10,742 Jun-2016 $10,750 $11,171 Jun-2017 $11,152 $13,170 Jun-2018 $11,599 $15,064 Jun-2019 $12,621 $16,633 Jun-2020 $12,995 $17,881 Jun-2021 $16,819 $25,175 Jun-2022 $16,019 $22,503 Jun-2023 $15,881 $26,912 Jun-2024 $16,409 $33,521 |
| Average Annual Return [Table Text Block] | Average Annual Total Returns 1 Year 5 Years 10 Years Bruce Fund 3.32% 5.39% 5.08% S&P 500 ® 24.56% 15.05% 12.86% 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. |
| Material Change Date | Jun. 30, 2024 |
| AssetsNet | $ 399,427,557 |
| Holdings Count | Holding | 41 |
| Advisory Fees Paid, Amount | $ 2,400,450 |
| InvestmentCompanyPortfolioTurnover | 8% |
| Additional Fund Statistics [Text Block] | Fund Statistics Net Assets $399,427,557 Number of Portfolio Holdings 41 Advisory Fee $2,400,450 Portfolio Turnover 8% |
| Holdings [Text Block] | Asset Weighting (% of total investments) Value Value Common Stocks 67.4% Convertible Bonds 1.2% Money Market Funds 27.9% U.S. Government & Agencies 3.5% |
| Material Fund Change [Text Block] | Material Fund Changes No material changes occurred during the year ended June 30, 2024. |
| Shareholder Report, Line Graph (Details) - USD ($) | 12 Months Ended | ||||||||||
| Jun. 30, 2014 | Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2015 | |
| C000031584 | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Bruce Fund | ||||||||||
| Account Value | $ 10,000 | $ 16,409 | $ 15,881 | $ 16,019 | $ 16,819 | $ 12,995 | $ 12,621 | $ 11,599 | $ 11,152 | $ 10,750 | $ 9,887 |
| 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 | $ 33,521 | $ 26,912 | $ 22,503 | $ 25,175 | $ 17,881 | $ 16,633 | $ 15,064 | $ 13,170 | $ 11,171 | $ 10,742 |
| Shareholder Report, Average Annual Return (Details) | 12 Months Ended | 60 Months Ended | 120 Months Ended | |
| Jun. 30, 2024 | Jun. 30, 2014 | Jun. 30, 2024 | Jun. 30, 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 | 3.32% | 5.39% | 5.08% | |
| S&P 500 Index | ||||
| Average Annual Return [Line Items] | ||||
| Line Graph and Table Measure Name | ®</sup> Index" id="sjs-C11">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 | 24.56% | 15.05% | 12.86% | |
| Shareholder Report, Holdings (Details) - C000031584 | Jun. 30, 2024 |
| 61747C707 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 27.90% |
| 023586506 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7% |
| 58933Y105 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.50% |
| 00287Y109 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.40% |
| 26441C204 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| 65339F101 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| 020002101 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| 125896100 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| 00206R102 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.30% |
| 002824100 | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.70% |
| Materials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.40% |
| Technology | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| Consumer Staples | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| U.S. Treasury Obligations | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.50% |
| Communications | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.70% |
| Financials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.80% |
| Industrials | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.70% |
| Utilities | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18.90% |
| Health Care | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 22.40% |
| Money Market Funds | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 27.90% |
| InvestmentType_Common Stocks | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.40% |
| InvestmentType_Convertible Bonds | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| InvestmentType_Money Market Funds | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
| InvestmentType_U.S. Government & Agencies | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
