LifePath Index Retirement Fund seeks to provide for retirement outcomes based on quantitatively measured risk. BFA employs a multi-dimensional approach to assess risk for LifePath Index Retirement Fund and to determine LifePath Index Retirement Fund’s allocation across asset classes. As part of this multi-dimensional approach, BFA aims to quantify risk using proprietary risk measurement tools that, among other things, analyze historical and forward-looking securities market data, including risk, asset class correlations, and expected returns. Under normal circumstances, the Fund intends to invest primarily in affiliated open‑end index funds and affiliated exchange-traded funds (“ETFs”).

Investor P [Member] Investment Strategy - Investor P - BLACKROCK LIFEPATH INDEX RETIREMENT FUND	Dec. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	Principal Investment Strategies of the Fund
Strategy Narrative [Text Block]	LifePath Index Retirement Fund allocates and reallocates its assets among a combination of equity and bond index funds and money market funds (the “Underlying Funds”) in proportions based on its own comprehensive investment strategy. LifePath Index Retirement Fund seeks to provide for retirement outcomes based on quantitatively measured risk. BFA employs a multi-dimensional approach to assess risk for LifePath Index Retirement Fund and to determine LifePath Index Retirement Fund’s allocation across asset classes. As part of this multi-dimensional approach, BFA aims to quantify risk using proprietary risk measurement tools that, among other things, analyze historical and forward-looking securities market data, including risk, asset class correlations, and expected returns. Under normal circumstances, the Fund intends to invest primarily in affiliated open‑end index funds and affiliated exchange-traded funds (“ETFs”). LifePath Index Retirement Fund will invest, under normal circumstances, at least 80% of its assets in securities or other financial instruments that are components of or have economic characteristics similar to the securities included in its custom benchmark index, the LifePath Index Retirement Fund Custom Benchmark. LifePath Index Retirement Fund is designed for investors expecting to retire or to begin withdrawing assets now or in the near future. The Fund employs a “passive” management approach, attempting to invest in a portfolio of assets whose performance is expected to match approximately the performance of the Fund’s custom benchmark index. Certain Underlying Funds may invest in real estate investment trusts (“REITs”), foreign securities, emerging market securities, below investment-grade bonds, infrastructure, commodities and derivative securities or instruments, such as options and futures, the value of which is derived from another security, a currency or an index, when seeking to match the performance of a particular market index. The Fund and certain Underlying Funds may also lend securities with a value up to 33¹⁄₃% of their respective total assets to financial institutions that provide cash or securities issued or guaranteed by the U.S. Government as collateral. Factors such as fund classifications, historical risk and performance, and the relationship to other Underlying Funds in the Fund are considered when selecting Underlying Funds. The specific Underlying Funds selected for the Fund are determined at BFA’s discretion and may change as deemed appropriate to allow the Fund to meet its investment objective. See the “Details About the Funds — Information About the Underlying Funds” section of the prospectus for a list of the Underlying Funds, their classification into equity, fixed income or money market funds and a brief description of their investment objectives and primary investment strategies. The Fund’s selection of Underlying Funds that track equity indexes may be further diversified by style (including both value and growth), market capitalization (including large cap, mid cap, small cap and emerging growth), region (including domestic and international (including emerging markets)) or other factors. The Fund’s selection of Underlying Funds that track fixed-income indexes may be further diversified by sector (including government, corporate, agency, and other sectors), duration (a calculation of the average life of a bond which measures its price risk), credit quality (including non‑investment grade debt or junk bonds), geographic location (including U.S. and foreign-issued securities), or other factors. Though BFA seeks to diversify the Fund, certain Underlying Funds may concentrate their investments in specific sectors or geographic regions or countries. The percentage allocation to the various styles of equity and fixed-income Underlying Funds is determined at the discretion of the investment team and can be changed to reflect the current market environment. Because the Fund is in its most conservative phase, its allocation generally does not become more conservative over time, although its allocation may change to maintain the Fund’s risk profile.

LifePath Index Retirement Fund will invest, under normal circumstances, at least 80% of its assets in securities or other financial instruments that are components of or have economic characteristics similar to the securities included in its custom benchmark index, the LifePath Index Retirement Fund Custom Benchmark. LifePath Index Retirement Fund is designed for investors expecting to retire or to begin withdrawing assets now or in the near future. The Fund employs a “passive” management approach, attempting to invest in a portfolio of assets whose performance is expected to match approximately the performance of the Fund’s custom benchmark index. Certain Underlying Funds may invest in real estate investment trusts (“REITs”), foreign securities, emerging market securities, below investment-grade bonds, infrastructure, commodities and derivative securities or instruments, such as options and futures, the value of which is derived from another security, a currency or an index, when seeking to match the performance of a particular market index. The Fund and certain Underlying Funds may also lend securities with a value up to 33¹⁄₃% of their respective total assets to financial institutions that provide cash or securities issued or guaranteed by the U.S. Government as collateral.

Factors such as fund classifications, historical risk and performance, and the relationship to other Underlying Funds in the Fund are considered when selecting Underlying Funds. The specific Underlying Funds selected for the Fund are determined at BFA’s discretion and may change as deemed appropriate to allow the Fund to meet its investment objective. See the “Details About the Funds — Information About the Underlying Funds” section of the prospectus for a list of the Underlying Funds, their classification into equity, fixed income or money market funds and a brief description of their investment objectives and primary investment strategies.

The Fund’s selection of Underlying Funds that track equity indexes may be further diversified by style (including both value and growth), market capitalization (including large cap, mid cap, small cap and emerging growth), region (including domestic and international (including emerging markets)) or other factors. The Fund’s selection of Underlying Funds that track fixed-income indexes may be further diversified by sector (including government, corporate, agency, and other sectors), duration (a calculation of the average life of a bond which measures its price risk), credit quality (including non‑investment grade debt or junk bonds), geographic location (including U.S. and foreign-issued securities), or other factors. Though BFA seeks to diversify the Fund, certain Underlying Funds may concentrate their investments in specific sectors or geographic regions or countries. The percentage allocation to the various styles of equity and fixed-income Underlying Funds is determined at the discretion of the investment team and can be changed to reflect the current market environment. Because the Fund is in its most conservative phase, its allocation generally does not become more conservative over time, although its allocation may change to maintain the Fund’s risk profile.