Investor P [Member] Fees and Expenses - Investor P [Member] - iShares Municipal Bond Index Fund	Dec. 31, 2025 USD ($)
Prospectus [Line Items]
Expense Heading [Optional Text]	Fees and Expenses of the Fund
Expense Narrative [Text Block]	This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to your Financial Intermediary (as defined below), which are not reflected in the table and example below. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Fund Advisors (“BFA”) or its affiliates. More information about these and other discounts is available from your Financial Intermediary and in the “Details About the Share Class” section on page 19 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-98 of Part II of the Fund’s Statement of Additional Information (the “SAI”).
Expense Breakpoint Discounts [Text]	You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Fund Advisors (“BFA”) or its affiliates.
Expense Breakpoint, Minimum Investment Required [Amount]	$ 25,000
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	The Total Annual Fund Operating Expenses and Other Expenses do not correlate to the ratios of expenses to average net assets given in the Fund’s most recent Annual Financial Statements and Additional Information, which do not include Acquired Fund Fees and Expenses.
Shareholder Fees Caption [Optional Text]	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Optional Text]	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Expenses Deferred Charges [Text Block]	A contingent deferred sales charge (“CDSC”) of 0.15% is assessed on certain redemptions of Investor P Shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $1,000,000 or more.
Expense Example [Heading]	Example:
Expense Example Narrative [Text Block]	This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Portfolio Turnover [Heading]	Portfolio Turnover:
Portfolio Turnover [Text Block]	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 38% of the average value of its portfolio.
Portfolio Turnover, Rate	38.00%

Investor P [Member] Fees and Expenses - Investor P [Member] - iShares Municipal Bond Index Fund

Dec. 31, 2025

USD ($)

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to your Financial Intermediary (as defined below), which are not reflected in the table and example below. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Fund Advisors (“BFA”) or its affiliates. More information about these and other discounts is available from your Financial Intermediary and in the “Details About the Share Class” section on page 19 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-98 of Part II of the Fund’s Statement of Additional Information (the “SAI”).

Expense Breakpoint Discounts [Text]

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Fund Advisors (“BFA”) or its affiliates.

Expense Breakpoint, Minimum Investment Required [Amount]

$ 25,000

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

The Total Annual Fund Operating Expenses and Other Expenses do not correlate to the ratios of expenses to average net assets given in the Fund’s most recent Annual Financial Statements and Additional Information, which do not include Acquired Fund Fees and Expenses.

Shareholder Fees Caption [Optional Text]

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Optional Text]

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Expenses Deferred Charges [Text Block]

A contingent deferred sales charge (“CDSC”) of 0.15% is assessed on certain redemptions of Investor P Shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $1,000,000 or more.

Expense Example [Heading]

Example:

Expense Example Narrative [Text Block]

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5%

return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio Turnover [Heading]

Portfolio Turnover:

Portfolio Turnover [Text Block]

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 38% of the average value of its portfolio.

Portfolio Turnover, Rate

38.00%