| Form N-CSR Cover | 6 Months Ended |
| Jun. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Master Investment Portfolio |
| Entity Central Index Key | 0000915092 |
| 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 | Master Investment Portfolio |
| Entity Central Index Key | 0000915092 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Money Market Master Portfolio | |
| Shareholder Report [Line Items] | |
| Fund Name | Money Market Master Portfolio |
| Class Name | Money Market Master Portfolio |
| No Trading Symbol Flag | true |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about Money Market Master Portfolio (the “Master Portfolio”) 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 Master Portfolio included within the BlackRock Cash Funds: Institutional’s additional information blackrock.com/fundreports (888) 204-3956 |
| Additional Information Phone Number | (888) 204-3956 |
| Additional Information Website | blackrock.com/fundreports |
| Expenses [Text Block] | What were the Master Portfolio costs for the last six months? (based on a hypothetical $10,000 investment) Master Portfolio name Costs of a $10,000 Costs paid as a percentage of a Money Market Master Portfolio $ 0.07 % |
| Expenses Paid, Amount | $ 4 |
| Expense Ratio, Percent | 0.07% |
| Net Assets | $ 67,071,900,496 |
| Holdings Count | Holdings | 303 |
| Additional Fund Statistics [Text Block] | Key Master Portfolio statistics Net Assets $ Number of Portfolio Holdings 303 |
| Holdings [Text Block] | What did the Master Portfolio invest in? (as of June 30, 2024) Portfolio composition Investment Type Percent of Certificates of Deposit 28.7% Commercial Paper 27.2 Repurchase Agreements 21.2 Time Deposits 17.1 U.S. Treasury Obligations 3.0 Corporate Bonds 0.7 Municipal Bonds 0.6 Other Assets Less Liabilities 1.5 |
| Treasury Money Market Master Portfolio | |
| Shareholder Report [Line Items] | |
| Fund Name | Treasury Money Market Master Portfolio |
| Class Name | Treasury Money Market Master Portfolio |
| No Trading Symbol Flag | true |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about Treasury Money Market Master Portfolio (the “Master Portfolio”) 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 Master Portfolio included within the BlackRock Cash Funds: Treasury’s additional information blackrock.com/fundreports (888) 204-3956 |
| Additional Information Phone Number | (888) 204-3956 |
| Additional Information Website | blackrock.com/fundreports |
| Expenses [Text Block] | What were the Master Portfolio costs for the last six months? (based on a hypothetical $10,000 investment) Master Portfolio name Costs of a $10,000 Costs paid as a percentage of a Treasury Money Market Master Portfolio $ 0.07 % |
| Expenses Paid, Amount | $ 4 |
| Expense Ratio, Percent | 0.07% |
| Net Assets | $ 22,269,628,777 |
| Holdings Count | Holdings | 116 |
| Additional Fund Statistics [Text Block] | Key Master Portfolio statistics Net Assets $ Number of Portfolio Holdings 116 |
| Holdings [Text Block] | What did the Master Portfolio invest in? (as of June 30, 2024) Portfolio composition Investment Type Percent of U.S. Treasury Obligations 52.6% Repurchase Agreements 43.2 Other Assets Less Liabilities 4.2 |
| S&P 500 Index Master Portfolio | |
| Shareholder Report [Line Items] | |
| Fund Name | S&P 500 Index Master Portfolio |
| Class Name | S&P 500 Index Master Portfolio |
| No Trading Symbol Flag | true |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about S&P 500 Index Master Portfolio (the “Master Portfolio”) 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 Master Portfolio included within the iShares S&P 500 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 Master Portfolio costs for the last six months? (based on a hypothetical $10,000 investment) Master Portfolio name Costs of a $10,000 Costs paid as a percentage of a S&P 500 Index Master Portfolio $ 0.01 % |
| Expenses Paid, Amount | $ 1 |
| Expense Ratio, Percent | 0.01% |
| Net Assets | $ 42,412,693,020 |
| Holdings Count | Holdings | 507 |
| Investment Company, Portfolio Turnover | 4% |
| Additional Fund Statistics [Text Block] | Key Master Portfolio statistics Net Assets $ Number of Portfolio Holdings 507 Portfolio Turnover Rate 4 % |
| Holdings [Text Block] | What did the Master Portfolio invest in? (as of June 30, 2024) Sector allocation Sector (a) Percent of Information Technology 32.0% Financials 12.3 Health Care 11.6 Consumer Discretionary 9.9 Communication Services 9.2 Industrials 8.0 Consumer Staples 5.7 Energy 3.6 Utilities 2.2 Materials 2.1 Other* 2.8 Short-Term Securities 0.8 Liabilities in Excess of Other Assets (0.2) Ten largest holdings Security Percent of (b) Microsoft Corp. 7.2% NVIDIA Corp. 6.5 Apple, Inc. 6.5 Amazon.com, Inc. 3.8 Meta Platforms, Inc., Class A 2.4 Alphabet, Inc., Class A 2.3 Alphabet, Inc., Class C 1.9 Berkshire Hathaway, Inc., Class B 1.6 Eli Lilly & Co. 1.6 Broadcom, Inc. 1.5 (a) For purposes of this report, sector sub-classifications may differ from those utilized for compliance purposes. (b) 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) Microsoft Corp. 7.2% NVIDIA Corp. 6.5 Apple, Inc. 6.5 Amazon.com, Inc. 3.8 Meta Platforms, Inc., Class A 2.4 Alphabet, Inc., Class A 2.3 Alphabet, Inc., Class C 1.9 Berkshire Hathaway, Inc., Class B 1.6 Eli Lilly & Co. 1.6 Broadcom, Inc. 1.5 (a) For purposes of this report, sector sub-classifications may differ from those utilized for compliance purposes. (b) Excludes short-term securities. * Ten largest sectors are presented. Additional sectors are found in Other. |
| Shareholder Report, Holdings (Details) | Jun. 30, 2024 | |
| S&P 500 Index Master Portfolio | Microsoft Corp. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 7.20% | [1] |
| S&P 500 Index Master Portfolio | NVIDIA Corp. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 6.50% | [1] |
| S&P 500 Index Master Portfolio | Apple, Inc. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 6.50% | [1] |
| S&P 500 Index Master Portfolio | Amazon.com, Inc. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 3.80% | [1] |
| S&P 500 Index Master Portfolio | Meta Platforms, Inc., Class A [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.40% | [1] |
| S&P 500 Index Master Portfolio | Alphabet, Inc., Class A [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.30% | [1] |
| S&P 500 Index Master Portfolio | Alphabet, Inc., Class C [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.90% | [1] |
| S&P 500 Index Master Portfolio | Berkshire Hathaway, Inc., Class B [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.60% | [1] |
| S&P 500 Index Master Portfolio | Eli Lilly & Co. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.60% | [1] |
| S&P 500 Index Master Portfolio | Broadcom, Inc. [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.50% | [1] |
| S&P 500 Index Master Portfolio | Information Technology Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 32% | [2] |
| S&P 500 Index Master Portfolio | Financial Services Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 12.30% | [2] |
| S&P 500 Index Master Portfolio | Healthcare Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 11.60% | [2] |
| S&P 500 Index Master Portfolio | Consumer Discretionary Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 9.90% | [2] |
| S&P 500 Index Master Portfolio | Communications Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 9.20% | [2] |
| S&P 500 Index Master Portfolio | Industrial Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 8% | [2] |
| S&P 500 Index Master Portfolio | Consumer Staples Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 5.70% | [2] |
| S&P 500 Index Master Portfolio | Energy Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 3.60% | [2] |
| S&P 500 Index Master Portfolio | Utilities Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.20% | [2] |
| S&P 500 Index Master Portfolio | Materials Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.10% | [2] |
| S&P 500 Index Master Portfolio | Unclassified Sector [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 2.80% | [2],[3] |
| S&P 500 Index Master Portfolio | Short Term Securities [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.80% | [2] |
| S&P 500 Index Master Portfolio | Liabilities in Excess of Other Assets [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | (0.20%) | [2] |
| Treasury Money Market Master Portfolio | U.S. Treasury Obligations [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 52.60% | |
| Treasury Money Market Master Portfolio | Repurchase Agreements [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 43.20% | |
| Treasury Money Market Master Portfolio | Other Assets Less Liabilities [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 4.20% | |
| Money Market Master Portfolio | U.S. Treasury Obligations [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 3% | |
| Money Market Master Portfolio | Repurchase Agreements [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 21.20% | |
| Money Market Master Portfolio | Other Assets Less Liabilities [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 1.50% | |
| Money Market Master Portfolio | Certificates of Deposit [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 28.70% | |
| Money Market Master Portfolio | Commercial Papers [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 27.20% | |
| Money Market Master Portfolio | Time Deposits [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 17.10% | |
| Money Market Master Portfolio | Corporate Bond Securities [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.70% | |
| Money Market Master Portfolio | Municipal Bond [Member] | ||
| Holdings [Line Items] | ||
| Percent of Net Asset Value | 0.60% | |
| [1]Excludes short-term securities.[2]For purposes of this report, sector sub-classifications may differ from those utilized for compliance purposes.[3]Ten largest sectors are presented. Additional sectors are found in Other. | ||
