BlackRock Funds III N-CSRS4 Sep 24Certified semi-annual shareholder report (management investment company)Financial data

Company Profile

Form N-CSR Cover

Form N-CSR Cover	6 Months Ended
Form N-CSR Cover	Jun. 30, 2024
Shareholder Report [Line Items]
Document Type	N-CSRS
Amendment Flag	false
Registrant Name	BlackRock Funds III
Entity Central Index Key	0000893818
Entity Investment Company Type	N-1A
Document Period End Date	Jun. 30, 2024

Shareholder Report

Shareholder Report	6 Months Ended
Shareholder Report	Jun. 30, 2024 USD ($) Holding
Shareholder Report [Line Items]
Document Type	N-CSRS
Amendment Flag	false
Registrant Name	BlackRock Funds III
Entity Central Index Key	0000893818
Entity Investment Company Type	N-1A
Document Period End Date	Jun. 30, 2024
BlackRock Diversified Equity Fund Institutional Shares
Shareholder Report [Line Items]
Fund Name	BlackRock Diversified Equity Fund
Class Name	Institutional Shares
Trading Symbol	BDVEX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about BlackRock Diversified Equity Fund (the “Fund”) 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]	The Fund invests all of its assets in the Diversified Equity Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. You can find additional information about the Fund at blackrock.com/fundreports (800)
Additional Information Phone Number	(800) 537-4942
Additional Information Website	blackrock.com/fundreports
Expenses [Text Block]	What were the Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Institutional Shares $ (a) 0.39 % (a) (a) Because the Fund invests all of its assets in the Mast er
Expenses Paid, Amount	$ 21	[1]
Expense Ratio, Percent	0.39%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Institutional Shares 15.58% 25.49% 14.66% 12.35% Russell 1000 ® 14.24 23.88 14.61 12.51
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	$ 999,081,867
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	61%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $999,081,867 Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 61 %
Updated Prospectus Web Address	blackrock.com
iShares MSCI Total International Index Fund - Institutional Shares
Shareholder Report [Line Items]
Fund Name	iShares MSCI Total International Index Fund
Class Name	Institutional Shares
Trading Symbol	BDOIX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares MSCI Total International Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the Total International ex U.S. Index Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Institutional Shares $ (a) 0.15 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 8	[1]
Expense Ratio, Percent	0.15%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Institutional Shares 5.57% 10.85% 5.28% 3.65% MSCI ACWI ex USA Index 5.69 11.62 5.55 3.84
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	$ 1,869,106,670
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	4%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $1,869,106,670 Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 %
Updated Prospectus Web Address	blackrock.com
iShares MSCI Total International Index Fund - Investor A Shares
Shareholder Report [Line Items]
Fund Name	iShares MSCI Total International Index Fund
Class Name	Investor A Shares
Trading Symbol	BDOAX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares MSCI Total International Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the Total International ex U.S. Index Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Investor A Shares $ (a) 0.41 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 21	[1]
Expense Ratio, Percent	0.41%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Investor A Shares 5.43% 10.56% 5.00% 3.38% MSCI ACWI ex USA Index 5.69 11.62 5.55 3.84
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	$ 1,869,106,670
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	4%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $1,869,106,670 Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 %
Updated Prospectus Web Address	blackrock.com
iShares MSCI Total International Index Fund - Class K Shares
Shareholder Report [Line Items]
Fund Name	iShares MSCI Total International Index Fund
Class Name	Class K Shares
Trading Symbol	BDOKX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares MSCI Total International Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the Total International ex U.S. Index Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Class K Shares $ (a) 0.10 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 5	[1]
Expense Ratio, Percent	0.10%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Class K Shares 5.61% 10.85% 5.32% 3.69% MSCI ACWI ex USA Index 5.69 11.62 5.55 3.84
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	$ 1,869,106,670
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	4%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $1,869,106,670 Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 %
Updated Prospectus Web Address	blackrock.com
iShares Russell 1000 Large-Cap Index Fund - Institutional Shares
Shareholder Report [Line Items]
Fund Name	iShares Russell 1000 Large-Cap Index Fund
Class Name	Institutional Shares
Trading Symbol	BRGNX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares Russell 1000 Large-Cap Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the Large Cap Index Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Institutional Shares $ (a) 0.12 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 6	[1]
Expense Ratio, Percent	0.12%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Institutional Shares 14.15% 23.77% 14.49% 12.38% Russell 1000® Index 14.24 23.88 14.61 12.51
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	$ 1,357,859,726
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	5%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 5 %
Updated Prospectus Web Address	blackrock.com
iShares Russell 1000 Large-Cap Index - Fund Investor A Shares
Shareholder Report [Line Items]
Fund Name	iShares Russell 1000 Large-Cap Index Fund
Class Name	Investor A Shares
Trading Symbol	BRGAX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares Russell 1000 Large-Cap Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the Large Cap Index Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Investor A Shares $ (a) 0.36 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 19	[1]
Expense Ratio, Percent	0.36%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Investor A Shares 14.02% 23.51% 14.20% 12.10% Russell 1000® Index 14.24 23.88 14.61 12.51
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	$ 1,357,859,726
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	5%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 5 %
Updated Prospectus Web Address	blackrock.com
iShares Russell 1000 Large-Cap Index Fund - Class K Shares
Shareholder Report [Line Items]
Fund Name	iShares Russell 1000 Large-Cap Index Fund
Class Name	Class K Shares
Trading Symbol	BRGKX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares Russell 1000 Large-Cap Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the Large Cap Index Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Class K Shares $ (a) 0.07 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 4	[1]
Expense Ratio, Percent	0.07%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Class K Shares 14.21% 23.87% 14.54% 12.44% Russell 1000® Index 14.24 23.88 14.61 12.51
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	$ 1,357,859,726
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	5%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 5 %
Updated Prospectus Web Address	blackrock.com
iShares U.S. Aggregate Bond Index Fund - Institutional Shares
Shareholder Report [Line Items]
Fund Name	iShares U.S. Aggregate Bond Index Fund
Class Name	Institutional Shares
Trading Symbol	BMOIX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares U.S. Aggregate Bond Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the U.S. Total Bond 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Institutional Shares $ (a) 0.10 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 5	[1]
Expense Ratio, Percent	0.10%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Institutional Shares (0.57)% 2.69% (0.27)% 1.25% Bloomberg U.S. Aggregate Bond Index (0.71) 2.63 (0.23) 1.35
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	$ 2,800,905,926
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	54%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 54 %
Updated Prospectus Web Address	blackrock.com
iShares U.S. Aggregate Bond Index Fund - Investor A Shares
Shareholder Report [Line Items]
Fund Name	iShares U.S. Aggregate Bond Index Fund
Class Name	Investor A Shares
Trading Symbol	BMOAX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares U.S. Aggregate Bond Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the U.S. Total Bond 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Investor A Shares $ (a) 0.35 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 17	[1]
Expense Ratio, Percent	0.35%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Investor A Shares (0.69)% 2.43% (0.50)% 1.00% Bloomberg U.S. Aggregate Bond Index (0.71) 2.63 (0.23) 1.35
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	$ 2,800,905,926
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	54%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 54 %
Updated Prospectus Web Address	blackrock.com
iShares U.S. Aggregate Bond Index Fund - Investor P Shares
Shareholder Report [Line Items]
Fund Name	iShares U.S. Aggregate Bond Index Fund
Class Name	Investor P Shares
Trading Symbol	BMOPX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares U.S. Aggregate Bond Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the U.S. Total Bond 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Investor P Shares $ (a) 0.35 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 17	[1]
Expense Ratio, Percent	0.35%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Investor P Shares (0.69)% 2.32% (0.53)% 0.98% Investor P Shares (with sales charge) (4.67) (1.77) (1.34) 0.57 Bloomberg U.S. Aggregate Bond Index (0.71) 2.63 (0.23) 1.35
Performance Inception Date	Aug. 06, 2018
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	$ 2,800,905,926
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	54%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 54 %
Updated Prospectus Web Address	blackrock.com
iShares U.S. Aggregate Bond Index Fund - Class K Shares
Shareholder Report [Line Items]
Fund Name	iShares U.S. Aggregate Bond Index Fund
Class Name	Class K Shares
Trading Symbol	WFBIX
Annual or Semi-Annual Statement [Text Block]	This semi-annual shareholder report contains important information about iShares U.S. Aggregate Bond Index Fund (the “Fund”) 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]	The Fund invests all of its assets in the U.S. Total Bond 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 Fund costs for the last six months? (based on a hypothetical $10,000 investment) Class name Costs of a $10,000 Costs paid as a percentage of a Class K Shares $ (a) 0.05 % (a) (a) Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Expenses Paid, Amount	$ 2	[1]
Expense Ratio, Percent	0.05%	[1]
Expenses Represent Both Master and Feeder [Text]	Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.
Performance Past Does Not Indicate Future [Text]	Past performance is not an indication of future results. Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.
Average Annual Return [Table Text Block]	Average annual total returns 6-Month 1 Year 5 Years 10 Years Class K Shares (0.54)% 2.63% (0.22)% 1.29% Bloomberg U.S. Aggregate Bond Index (0.71) 2.63 (0.23) 1.35
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	$ 2,800,905,926
Holdings Count \| Holding	1
Investment Company, Portfolio Turnover	54%
Additional Fund Statistics [Text Block]	Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 54 %
Updated Prospectus Web Address	blackrock.com

[1]Because the Fund invests all of its assets in the Master Portfolio, the expense example reflects the net expenses of both the Fund and the Master Portfolio.

Shareholder Report, Average Ann

Shareholder Report, Average Annual Return (Details)	6 Months Ended	12 Months Ended	60 Months Ended	120 Months Ended
Shareholder Report, Average Annual Return (Details)	Jun. 30, 2024	Jun. 30, 2024	Jun. 30, 2024	Jun. 30, 2024
iShares U.S. Aggregate Bond Index Fund - Class K Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Class K Shares
Average Annual Return, Percent	(0.54%)	2.63%	(0.22%)	1.29%
iShares U.S. Aggregate Bond Index Fund - Investor P Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor P Shares (with sales charge)
Average Annual Return, Percent	(4.67%)	(1.77%)	(1.34%)	0.57%
iShares U.S. Aggregate Bond Index Fund - Investor A Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor A Shares
Average Annual Return, Percent	(0.69%)	2.43%	(0.50%)	1%
iShares U.S. Aggregate Bond Index Fund - Institutional Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Institutional Shares
Average Annual Return, Percent	(0.57%)	2.69%	(0.27%)	1.25%
iShares Russell 1000 Large-Cap Index Fund - Class K Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Class K Shares
Average Annual Return, Percent	14.21%	23.87%	14.54%	12.44%
iShares Russell 1000 Large-Cap Index - Fund Investor A Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor A Shares
Average Annual Return, Percent	14.02%	23.51%	14.20%	12.10%
iShares Russell 1000 Large-Cap Index Fund - Institutional Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Institutional Shares
Average Annual Return, Percent	14.15%	23.77%	14.49%	12.38%
iShares MSCI Total International Index Fund - Class K Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Class K Shares
Average Annual Return, Percent	5.61%	10.85%	5.32%	3.69%
iShares MSCI Total International Index Fund - Investor A Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor A Shares
Average Annual Return, Percent	5.43%	10.56%	5%	3.38%
iShares MSCI Total International Index Fund - Institutional Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Institutional Shares
Average Annual Return, Percent	5.57%	10.85%	5.28%	3.65%
BlackRock Diversified Equity Fund Institutional Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Institutional Shares
Average Annual Return, Percent	15.58%	25.49%	14.66%	12.35%
Without Sales Load [Member] \| iShares U.S. Aggregate Bond Index Fund - Investor P Shares
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Investor P Shares
Average Annual Return, Percent	(0.69%)	2.32%	(0.53%)	0.98%
Bloomberg U.S. Aggregate Bond Index [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Bloomberg U.S. Aggregate Bond Index
Average Annual Return, Percent	(0.71%)	2.63%	(0.23%)	1.35%
Russell 1000 Index [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	Russell 1000® Index
Average Annual Return, Percent	14.24%	23.88%	14.61%	12.51%
MSCI ACWI ex USA Index [Member]
Average Annual Return [Line Items]
Line Graph and Table Measure Name	MSCI ACWI ex USA Index
Average Annual Return, Percent	5.69%	11.62%	5.55%	3.84%