| Form N-CSR Cover | 12 Months Ended |
| Dec. 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | BNY Mellon Stock Index Fund, Inc. |
| Entity Central Index Key | 0000846800 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Dec. 31, 2024 |
| Shareholder Report | 12 Months Ended |
| Dec. 31, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | BNY Mellon Stock Index Fund, Inc. |
| Entity Central Index Key | 0000846800 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Dec. 31, 2024 |
| C000005028 [Member] | |
| Shareholder Report [Line Items] | |
| Fund Name | BNY Mellon Stock Index Fund, Inc. |
| Class Name | Initial Shares |
| No Trading Symbol Flag | true |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about BNY Mellon Stock Index Fund, Inc. (the “Fund”) for the period of January 1, 2024 to December 31, 2024. |
| Shareholder Report Annual or Semi-Annual | annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.bny.com/investments/us/en/intermediary/products/variable-products.html#funds-table-tabs1 |
| Additional Information Phone Number | 1-800-373-9387 |
| Additional Information Email | info@bny.com |
| Additional Information Website | www.bny.com/investments/us/en/intermediary/products/variable-products.html#funds-table-tabs1 |
| Expenses [Text Block] | What were the Fund’s costs for the last year ? (based on a hypothetical $10,000 investment) Share Class Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Initial Shares $ 0.27 % |
| Expenses Paid, Amount | $ 30 |
| Expense Ratio, Percent | 0.27% |
| Factors Affecting Performance [Text Block] | How did the Fund perform last year ? For the 12-month period ended December 31, 2024, the Fund’s Initial Shares returned 24.67%. In comparison, the S&P 500 ® What affected the Fund’s performance? The U.S. equity markets posted healthy double-digit gains due to resilient economic growth, moderating inflation and rising corporate profits. Large-cap stocks outperformed mid- and small-cap shares by a considerable margin. Growth-oriented stocks outperformed value-oriented shares due to the improving economic outlook, rising corporate profits, and the prospect of lower interest rates. The best-performing sectors included communication services and information technology, driven by investor enthusiasm for artificial intelligence-related companies. Financials also outperformed due to prospects for reduced regulatory oversight. Materials was the only sector to post negative performance during the period. The difference in returns between the Fund and the Index resulted primarily from transaction costs and operating expenses that are not reflected in index results. Not FDIC Insured. Not Bank-Guaranteed. May Lose Value |
| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. |
| Line Graph [Table Text Block] | How did the Fund perform over the past 10 years? The Fund’s past performance is not a good predictor of the Fund’s future performance. Cumulative Performance from January 1 , 2014 through December 31, 2024 Initial Investment of $10,000 The above graph compares a hypothetical $10,000 investment in the Fund’s Initial Shares to a hypothetical investment of $10,000 made in the S&P 500 ® |
| Average Annual Return [Table Text Block] | AVERAGE ANNUAL TOTAL RETURNS (AS OF 12/31/24 ) Share Class 1YR 5YR 10YR Initial Shares 24.67 % 14.21 % 12.81 % S&P 500 ® 25.02 % 14.52 % 13.10 % |
| 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. |
| Updated Performance Information Location [Text Block] | For more current information visit www.bny.com/investments/us/en/intermediary/products/variable-products.html#funds-table-tabs1 . |
| Net Assets | $ 3,443,000,000 |
| Holdings Count | Holding | 506 |
| Advisory Fees Paid, Amount | $ 7,909,942 |
| Investment Company Portfolio Turnover | 2.65% |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (AS OF 12/31/24 ) Total Advisory Fee Paid During $ 506 $ 2.65 % Not FDIC Insured. Not Bank-Guaranteed. May Lose Value |
| Holdings [Text Block] | Portfolio Holdings (as of 12/31/24 ) Top Ten Holdings (Based on Net Assets) * * Excludes money market funds or other short-term securities held for the investment of cash and cash collateral for securities loaned, if any. Sector Allocation (Based on Net Assets) |
| Largest Holdings [Text Block] | Top Ten Holdings (Based on Net Assets) * * Excludes money market funds or other short-term securities held for the investment of cash and cash collateral for securities loaned, if any. |
| C000005029 [Member] | |
| Shareholder Report [Line Items] | |
| Fund Name | BNY Mellon Stock Index Fund, Inc. |
| Class Name | Service Shares |
| No Trading Symbol Flag | true |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about BNY Mellon Stock Index Fund, Inc. (the “Fund”) for the period of January 1, 2024 to December 31, 2024. |
| Shareholder Report Annual or Semi-Annual | annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.bny.com/investments/us/en/intermediary/products/variable-products.html#funds-table-tabs1 |
| Additional Information Phone Number | 1-800-373-9387 |
| Additional Information Email | info@bny.com |
| Additional Information Website | www.bny.com/investments/us/en/intermediary/products/variable-products.html#funds-table-tabs1 |
| Expenses [Text Block] | What were the Fund’s costs for the last year ? (based on a hypothetical $10,000 investment) Share Class Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Service Shares $ 0.52 % |
| Expenses Paid, Amount | $ 58 |
| Expense Ratio, Percent | 0.52% |
| Factors Affecting Performance [Text Block] | How did the Fund perform last year ? For the 12-month period ended December 31, 2024, the Fund’s Service Shares returned 24.34%. In comparison, the S&P 500 ® What affected the Fund’s performance? The U.S. equity markets posted healthy double-digit gains due to resilient economic growth, moderating inflation and rising corporate profits. Large-cap stocks outperformed mid- and small-cap shares by a considerable margin. Growth-oriented stocks outperformed value-oriented shares due to the improving economic outlook, rising corporate profits, and the prospect of lower interest rates. The best-performing sectors included communication services and information technology, driven by investor enthusiasm for artificial intelligence-related companies. Financials also outperformed due to prospects for reduced regulatory oversight. Materials was the only sector to post negative performance during the period. The difference in returns between the Fund and the Index resulted primarily from transaction costs and operating expenses that are not reflected in index results. Not FDIC Insured. Not Bank-Guaranteed. May Lose Value |
| Performance Past Does Not Indicate Future [Text] | The Fund’s past performance is not a good predictor of the Fund’s future performance. |
| Line Graph [Table Text Block] | How did the Fund perform over the past 10 years? The Fund’s past performance is not a good predictor of the Fund’s future performance. Cumulative Performance from January 1 , 2014 through December 31, 2024 Initial Investment of $10,000 The above graph compares a hypothetical $10,000 investment in the Fund’s Service Shares to a hypothetical investment of $10,000 made in the S&P 500 ® |
| Average Annual Return [Table Text Block] | AVERAGE ANNUAL TOTAL RETURNS (AS OF 12/31/24 ) Share Class 1YR 5YR 10YR Service Shares 24.34 % 13.92 % 12.53 % S&P 500 ® 25.02 % 14.52 % 13.10 % |
| 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. |
| Updated Performance Information Location [Text Block] | For more current information visit www.bny.com/investments/us/en/intermediary/products/variable-products.html#funds-table-tabs1 |
| Net Assets | $ 3,443,000,000 |
| Holdings Count | Holding | 506 |
| Advisory Fees Paid, Amount | $ 7,909,942 |
| Investment Company Portfolio Turnover | 2.65% |
| Additional Fund Statistics [Text Block] | KEY FUND STATISTICS (AS OF 12/31/24 ) Total Advisory Fee Paid During $ 506 $ 2.65 % Not FDIC Insured. Not Bank-Guaranteed. May Lose Value |
| Holdings [Text Block] | Portfolio Holdings (as of 12/31/24 ) Top Ten Holdings (Based on Net Assets) * * Excludes money market funds or other short-term securities held for the investment of cash and cash collateral for securities loaned, if any. Sector Allocation (Based on Net Assets) |
| Largest Holdings [Text Block] | Top Ten Holdings (Based on Net Assets) * * Excludes money market funds or other short-term securities held for the investment of cash and cash collateral for securities loaned, if any. |
| Shareholder Report, Line Graph (Details) - USD ($) | 12 Months Ended | 60 Months Ended | 120 Months Ended | ||||||||||
| Dec. 31, 2024 | Dec. 31, 2024 | 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 | Dec. 31, 2014 | |
| C000005028 [Member] | |||||||||||||
| Account Value [Line Items] | |||||||||||||
| Line Graph and Table Measure Name | Initial Shares | ||||||||||||
| Account Value | $ 33,371 | $ 33,371 | $ 33,371 | $ 26,767 | $ 21,256 | $ 26,023 | $ 20,265 | $ 17,173 | $ 13,091 | $ 13,727 | $ 11,294 | $ 10,111 | $ 10,000 |
| Average Annual Return, Percent | 24.67% | 14.21% | 12.81% | ||||||||||
| C000005029 [Member] | |||||||||||||
| Account Value [Line Items] | |||||||||||||
| Line Graph and Table Measure Name | Service Shares | ||||||||||||
| Account Value | $ 32,548 | $ 32,548 | $ 32,548 | 26,178 | 20,842 | 25,580 | 19,967 | 16,962 | 12,964 | 13,625 | 11,241 | 10,087 | 10,000 |
| Average Annual Return, Percent | 24.34% | 13.92% | 12.53% | ||||||||||
| Standard & Poor's 500 Index [Member] | |||||||||||||
| Account Value [Line Items] | |||||||||||||
| Line Graph and Table Measure Name | S&P 500® Index | ||||||||||||
| Account Value | $ 34,237 | $ 34,237 | $ 34,237 | $ 27,388 | $ 21,690 | $ 26,483 | $ 20,578 | $ 17,380 | $ 13,221 | $ 13,826 | $ 11,350 | $ 10,139 | $ 10,000 |
| Average Annual Return, Percent | 25.02% | 14.52% | 13.10% |
| Shareholder Report, Holdings (Details) | Dec. 31, 2024 | |
| C000005028 [Member] | Apple Inc [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 7.40% | [1] |
| C000005028 [Member] | NVIDIA Corp [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 6.50% | [1] |
| C000005028 [Member] | Microsoft Corp [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 6.20% | [1] |
| C000005028 [Member] | Amazon com Inc [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 4% | [1] |
| C000005028 [Member] | Meta Platforms Inc Cl A [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.50% | [1] |
| C000005028 [Member] | Tesla Inc [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.20% | [1] |
| C000005028 [Member] | Alphabet Inc Cl A [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.20% | [1] |
| C000005028 [Member] | Broadcom Inc [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.10% | [1] |
| C000005028 [Member] | Alphabet Inc Cl C [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.80% | [1] |
| C000005028 [Member] | Berkshire Hathaway Inc Cl B [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.60% | [1] |
| C000005028 [Member] | Energy Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 3.10% | |
| C000005028 [Member] | Financial Services Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 13.30% | |
| C000005028 [Member] | Healthcare Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 9.90% | |
| C000005028 [Member] | Real Estate Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2% | |
| C000005028 [Member] | Communications Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 9.20% | |
| C000005028 [Member] | Consumer Discretionary Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 11% | |
| C000005028 [Member] | Consumer Staples Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 5.40% | |
| C000005028 [Member] | Industrial Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 8% | |
| C000005028 [Member] | Information Technology Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 31.80% | |
| C000005028 [Member] | Materials Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.90% | |
| C000005028 [Member] | Utilities Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.30% | |
| C000005028 [Member] | Investment Companies [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2% | |
| C000005028 [Member] | Net Other Assets and Liabilities [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.10% | |
| C000005029 [Member] | Apple Inc [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 7.40% | [2] |
| C000005029 [Member] | NVIDIA Corp [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 6.50% | [2] |
| C000005029 [Member] | Microsoft Corp [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 6.20% | [2] |
| C000005029 [Member] | Amazon com Inc [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 4% | [2] |
| C000005029 [Member] | Meta Platforms Inc Cl A [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.50% | [2] |
| C000005029 [Member] | Tesla Inc [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.20% | [2] |
| C000005029 [Member] | Alphabet Inc Cl A [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.20% | [2] |
| C000005029 [Member] | Broadcom Inc [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.10% | [2] |
| C000005029 [Member] | Alphabet Inc Cl C [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.80% | [2] |
| C000005029 [Member] | Berkshire Hathaway Inc Cl B [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.60% | [2] |
| C000005029 [Member] | Energy Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 3.10% | |
| C000005029 [Member] | Financial Services Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 13.30% | |
| C000005029 [Member] | Healthcare Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 9.90% | |
| C000005029 [Member] | Real Estate Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2% | |
| C000005029 [Member] | Communications Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 9.20% | |
| C000005029 [Member] | Consumer Discretionary Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 11% | |
| C000005029 [Member] | Consumer Staples Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 5.40% | |
| C000005029 [Member] | Industrial Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 8% | |
| C000005029 [Member] | Information Technology Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 31.80% | |
| C000005029 [Member] | Materials Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.90% | |
| C000005029 [Member] | Utilities Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.30% | |
| C000005029 [Member] | Investment Companies [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2% | |
| C000005029 [Member] | Net Other Assets and Liabilities [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.10% | |
| [1]Excludes money market funds or other short-term securities held for the investment of cash and cash collateral for securities loaned, if any.[2]Excludes money market funds or other short-term securities held for the investment of cash and cash collateral for securities loaned, if any. | ||
