| Form N-CSR Cover | 6 Months Ended |
| Jun. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Quantitative Master Series LLC |
| Entity Central Index Key | 0001025836 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Shareholder Report | 6 Months Ended |
| Jun. 30, 2024 USD ($) Holdings | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Quantitative Master Series LLC |
| Entity Central Index Key | 0001025836 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Master Small Cap Index Series | |
| Shareholder Report [Line Items] | |
| Fund Name | Master Small Cap Index Series |
| Class Name | Master Small Cap Index Series |
| No Trading Symbol Flag | true |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about Master Small Cap Index Series (the “Series”) for the period of January 1, 2024 to June 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Series included within the iShares Russell 2000 Small-Cap Index Fund’s additional information blackrock.com/fundreports (800) 441-7762 |
| Additional Information Phone Number | (800) 441-7762 |
| Additional Information Website | blackrock.com/fundreports |
| Expenses [Text Block] | What were the Series costs for the last six months? (based on a hypothetical $10,000 investment) Series name Costs of a $10,000 Costs paid as a percentage of a Master Small Cap Index Series $ 0.02 % |
| Expenses Paid, Amount | $ 1 |
| Expense Ratio, Percent | 0.02% |
| Performance Past Does Not Indicate Future [Text] | Past performance is not an indication of future results. |
| No Deduction of Taxes [Text Block] | Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares. |
| Updated Performance Information Location [Text Block] | Visit blackrock.com |
| Net Assets | $ 4,982,925,751 |
| Holdings Count | Holdings | 2,145 |
| Investment Company, Portfolio Turnover | 18% |
| Additional Fund Statistics [Text Block] | Key Series statistics Net Assets $ % Number of Portfolio Holdings $ % Portfolio Turnover Rate $ % |
| Holdings [Text Block] | What did the Series invest in? (as of June 30, 2024) Sector allocation Sector (a) Percent of (b)(c) Health Care 17.0 ) % Industrials 16.9 ) % Financials 16.2 ) % Information Technology 13.1 ) % Consumer Discretionary 9.8 ) % Energy 6.5 ) % Real Estate 5.9 ) % Materials 4.5 ) % Consumer Staples 2.7 ) % Utilities 2.7 ) % Other* 3.1 ) % Short-Term Securities 9.2 ) % Liabilities in Excess of Other Assets (7.6 ) % Ten largest holdings Security Percent of (b)(c) iShares Russell 2000 ETF 0.7 % Insmed, Inc. 0.4 % FTAI Aviation Ltd. 0.4 % Abercrombie & Fitch Co., Class A 0.4 % Fabrinet 0.4 % Sprouts Farmers Market, Inc. 0.3 % Vaxcyte, Inc. 0.3 % Applied Industrial Technologies, Inc. 0.3 % Fluor Corp. 0.3 % HealthEquity, Inc. 0.3 % (a) For purposes of this report, sector sub-classifications may differ from those utilized for compliance purposes. (b) Excludes underlying investment in total return swaps. (c) Excludes short-term securities. * Ten largest sectors are presented. Additional sectors are found in Other. |
| Largest Holdings [Text Block] | Ten largest holdings Security Percent of (b)(c) iShares Russell 2000 ETF 0.7 % Insmed, Inc. 0.4 % FTAI Aviation Ltd. 0.4 % Abercrombie & Fitch Co., Class A 0.4 % Fabrinet 0.4 % Sprouts Farmers Market, Inc. 0.3 % Vaxcyte, Inc. 0.3 % Applied Industrial Technologies, Inc. 0.3 % Fluor Corp. 0.3 % HealthEquity, Inc. 0.3 % (a) For purposes of this report, sector sub-classifications may differ from those utilized for compliance purposes. (b) Excludes underlying investment in total return swaps. (c) Excludes short-term securities. * Ten largest sectors are presented. Additional sectors are found in Other. |
| Updated Prospectus Web Address | blackrock.com |
| Shareholder Report, Holdings (Details) - Master Small Cap Index Series | Jun. 30, 2024 | [1],[2] |
| iShares Russell 2000 ETF [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.70% | |
| Insmed, Inc. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.40% | |
| FTAI Aviation Ltd. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.40% | |
| Abercrombie & Fitch Co., Class A [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.40% | |
| Fabrinet [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.40% | |
| Sprouts Farmers Market, Inc. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.30% | |
| Vaxcyte, Inc. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.30% | |
| Applied Industrial Technologies, Inc. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.30% | |
| Fluor Corp. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.30% | |
| HealthEquity, Inc. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.30% | |
| Healthcare Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 17% | [3] |
| Industrial Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 16.90% | [3] |
| Financial Services Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 16.20% | [3] |
| Information Technology Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 13.10% | [3] |
| Consumer Discretionary Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 9.80% | [3] |
| Energy Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 6.50% | [3] |
| Real Estate Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 5.90% | [3] |
| Materials Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 4.50% | [3] |
| Consumer Staples Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.70% | [3] |
| Utilities Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.70% | [3] |
| Other [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 3.10% | [3],[4] |
| Short Term Securities [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 9.20% | |
| Liabilities in Excess of Other Assets [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | (7.60%) | |
| [1]Excludes short-term securities.[2]Excludes underlying investment in total return swaps.[3]For purposes of this report, sector sub-classifications may differ from those utilized for compliance purposes.[4]Ten largest sectors are presented. Additional sectors are found in Other. | ||
