Shareholder Report | 6 Months Ended |
Jun. 30, 2024 USD ($) Holdings |
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 Cash Funds: Institutional - SL Agency Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | BlackRock Cash Funds: Institutional | |
Class Name | SL Agency Shares | |
Trading Symbol | BISXX | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about BlackRock Cash Funds: Institutional (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 Money Market Master Portfolio 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 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 SL Agency Shares $ (a) 0.09 % (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 | 0.09% | [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. | |
Net Assets | $ 66,762,107,813 | |
Holdings Count | Holdings | 1 | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 | |
BlackRock Cash Funds: Treasury Institutional Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | BlackRock Cash Funds: Treasury | |
Class Name | Institutional Shares | |
Trading Symbol | BRIXX | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about BlackRock Cash Funds: Treasury (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 Treasury Money Market Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. 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 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. | |
Net Assets | $ 20,463,878,782 | |
Holdings Count | Holdings | 1 | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 | |
BlackRock Cash Funds: Treasury SL Agency Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | BlackRock Cash Funds: Treasury | |
Class Name | SL Agency Shares | |
Trading Symbol | XTSLA | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about BlackRock Cash Funds: Treasury (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 Treasury Money Market Master Portfolio (the “Master Portfolio”), a series of Master Investment Portfolio. 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 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 SL Agency Shares $ (a) 0.09 % (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 | 0.09% | [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. | |
Net Assets | $ 20,463,878,782 | |
Holdings Count | Holdings | 1 | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 | |
iShares S&P 500 Index Fund Institutional Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | iShares S&P 500 Index Fund | |
Class Name | Institutional Shares | |
Trading Symbol | BSPIX | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about iShares S&P 500 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 S&P 500 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. | |
Average Annual Return [Table Text Block] | Average annual total returns 6-Month 1 Year 5 Years 10 Years Institutional Shares 15.22% 24.41% 14.94% 12.75% S&P 500 ® 15.29 24.56 15.05 12.86 | |
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 | $ 41,780,034,318 | |
Holdings Count | Holdings | 1 | |
Investment Company, Portfolio Turnover | 4% | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 % | |
Updated Prospectus Web Address | blackrock.com | |
iShares S&P 500 Index Fund Service Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | iShares S&P 500 Index Fund | |
Class Name | Service Shares | |
Trading Symbol | BSPSX | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about iShares S&P 500 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 S&P 500 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 Service Shares $ (a) 0.22 % (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 | $ 12 | [1] |
Expense Ratio, Percent | 0.22% | [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. | |
Average Annual Return [Table Text Block] | Average annual total returns 6-Month 1 Year 5 Years 10 Years Service Shares 15.15% 24.25% 14.80% 12.61% S&P 500 ® 15.29 24.56 15.05 12.86 | |
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 | $ 41,780,034,318 | |
Holdings Count | Holdings | 1 | |
Investment Company, Portfolio Turnover | 4% | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 % | |
Updated Prospectus Web Address | blackrock.com | |
iShares S&P 500 Index Fund Investor A Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | iShares S&P 500 Index Fund | |
Class Name | Investor A Shares | |
Trading Symbol | BSPAX | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about iShares S&P 500 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 S&P 500 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 | $ 19 | [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. | |
Average Annual Return [Table Text Block] | Average annual total returns 6-Month 1 Year 5 Years 10 Years Investor A Shares 15.07% 24.09% 14.65% 12.47% S&P 500 ® 15.29 24.56 15.05 12.86 | |
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 | $ 41,780,034,318 | |
Holdings Count | Holdings | 1 | |
Investment Company, Portfolio Turnover | 4% | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 % | |
Updated Prospectus Web Address | blackrock.com | |
iShares S&P 500 Index Fund Investor P Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | iShares S&P 500 Index Fund | |
Class Name | Investor P Shares | |
Trading Symbol | BSPPX | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about iShares S&P 500 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 S&P 500 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 | $ 19 | [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. | |
Average Annual Return [Table Text Block] | Average annual total returns 6-Month 1 Year 5 Years 10 Years Investor P Shares 15.07% 24.09% 14.65% 12.47% Investor P Shares (with sales charge) 9.03 17.58 13.42 11.86 S&P 500 ® 15.29 24.56 15.05 12.86 | |
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 | $ 41,780,034,318 | |
Holdings Count | Holdings | 1 | |
Investment Company, Portfolio Turnover | 4% | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 % | |
Updated Prospectus Web Address | blackrock.com | |
iShares S&P 500 Index Fund Class G Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | iShares S&P 500 Index Fund | |
Class Name | Class G Shares | |
Trading Symbol | BSPGX | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about iShares S&P 500 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 S&P 500 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 G Shares $ (a) 0.01 % (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 | $ 1 | [1] |
Expense Ratio, Percent | 0.01% | [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 | |
Average Annual Return [Table Text Block] | Average annual total returns 6-Month 1 Year 5 Years 10 Years Class G Shares 15.27% 24.51% 15.04% 12.84% S&P 500 ® 15.29 24.56 15.05 12.86 | |
Performance Inception Date | Jul. 01, 2019 | |
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 | $ 41,780,034,318 | |
Holdings Count | Holdings | 1 | |
Investment Company, Portfolio Turnover | 4% | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 % | |
Updated Prospectus Web Address | blackrock.com | |
iShares S&P 500 Index Fund Class K Shares | | |
Shareholder Report [Line Items] | | |
Fund Name | iShares S&P 500 Index Fund | |
Class Name | Class K Shares | |
Trading Symbol | WFSPX | |
Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains important information about iShares S&P 500 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 S&P 500 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) 0.03 % (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 | 0.03% | [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. | |
Average Annual Return [Table Text Block] | Average annual total returns 6-Month 1 Year 5 Years 10 Years Class K Shares 15.26% 24.49% 15.02% 12.83% S&P 500 ® 15.29 24.56 15.05 12.86 | |
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 | $ 41,780,034,318 | |
Holdings Count | Holdings | 1 | |
Investment Company, Portfolio Turnover | 4% | |
Additional Fund Statistics [Text Block] | Key Fund statistics Net Assets $ Number of Portfolio Holdings 1 Portfolio Turnover Rate of the Master Portfolio 4 % | |
Updated Prospectus Web Address | blackrock.com | |
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[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. |