XML 8 R2.htm IDEA: XBRL DOCUMENT v3.26.1
Shareholder Report
6 Months Ended
Apr. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name BlackRock Liquidity Funds
Entity Central Index Key 0000097098
Entity Investment Company Type N-1A
Document Period End Date Apr. 30, 2026
C000003948  
Shareholder Report [Line Items]  
Fund Name BlackRock Select Treasury Based Liquidity Fund
Class Name Institutional Shares
Trading Symbol TFFXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Select Treasury Based Liquidity Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Institutional Shares
$8
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 8
Expense Ratio, Percent 0.17% [1]
AssetsNet $ 5,700,497,562
Holdings Count | Holding 24
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$5,700,497,562
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
24
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.53%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.53%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.6%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
46.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
C000003942  
Shareholder Report [Line Items]  
Fund Name BlackRock Select Treasury Based Liquidity Fund
Class Name Administration Shares
Trading Symbol BFTXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Select Treasury Based Liquidity Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Administration Shares
$13
0.27%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 13
Expense Ratio, Percent 0.27% [2]
AssetsNet $ 5,700,497,562
Holdings Count | Holding 24
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$5,700,497,562
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
24
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.43%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.43%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.6%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
46.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
C000003943  
Shareholder Report [Line Items]  
Fund Name BlackRock Select Treasury Based Liquidity Fund
Class Name Cash Management Shares
Trading Symbol BFMXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Select Treasury Based Liquidity Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Cash Management Shares
$33
0.67%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 33
Expense Ratio, Percent 0.67% [3]
AssetsNet $ 5,700,497,562
Holdings Count | Holding 24
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$5,700,497,562
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
24
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.02%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.02%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.6%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
46.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
C000003949  
Shareholder Report [Line Items]  
Fund Name BlackRock Select Treasury Based Liquidity Fund
Class Name Dollar Shares
Trading Symbol TSDXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Select Treasury Based Liquidity Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Dollar Shares
$21
0.42%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 21
Expense Ratio, Percent 0.42% [4]
AssetsNet $ 5,700,497,562
Holdings Count | Holding 24
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$5,700,497,562
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
24
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.28%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.28%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.6%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
46.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
C000231604  
Shareholder Report [Line Items]  
Fund Name BlackRock Select Treasury Based Liquidity Fund
Class Name Mischler Financial Group Shares
Trading Symbol EDUXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Select Treasury Based Liquidity Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Mischler Financial Group Shares
$8
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 8
Expense Ratio, Percent 0.17% [5]
AssetsNet $ 5,700,497,562
Holdings Count | Holding 24
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$5,700,497,562
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
24
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.52%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.52%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.6%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
46.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
C000237278  
Shareholder Report [Line Items]  
Fund Name BlackRock Select Treasury Based Liquidity Fund
Class Name Stern Brothers Shares
Trading Symbol SIGXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Select Treasury Based Liquidity Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Stern Brothers Shares
$8
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 8
Expense Ratio, Percent 0.17% [6]
AssetsNet $ 5,700,497,562
Holdings Count | Holding 24
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$5,700,497,562
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
24
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.53%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.53%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.6%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
46.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
C000238343  
Shareholder Report [Line Items]  
Fund Name BlackRock Select Treasury Based Liquidity Fund
Class Name Tigress Shares
Trading Symbol EVEXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BlackRock Select Treasury Based Liquidity Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Tigress Shares
$8
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 8
Expense Ratio, Percent 0.17% [7]
AssetsNet $ 5,700,497,562
Holdings Count | Holding 24
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$5,700,497,562
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
24
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.53%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.53%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.6%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
46.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
C000003928  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Institutional Shares
Trading Symbol TFDXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Institutional Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [8]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003923  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Administration Shares
Trading Symbol BLFXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Administration Shares
$14
0.27%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 14
Expense Ratio, Percent 0.27% [9]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.44%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.44%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003927  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Capital Shares
Trading Symbol BFCXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Capital Shares
$11
0.22%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 11
Expense Ratio, Percent 0.22% [10]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.49%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.49%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003924  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Cash Management Shares
Trading Symbol BFFXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Cash Management Shares
$33
0.67%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 33
Expense Ratio, Percent 0.67% [11]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.05%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.05%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003931  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Cash Reserve Shares
Trading Symbol BFRXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Cash Reserve Shares
$28
0.57%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 28
Expense Ratio, Percent 0.57% [12]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.14%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.14%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003930  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Dollar Shares
Trading Symbol TDDXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Dollar Shares
$21
0.42%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 21
Expense Ratio, Percent 0.42% [13]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.29%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.29%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000252320  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Great Pacific Shares
Trading Symbol GPAXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Great Pacific Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [14]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000223514  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Mischler Financial Group Shares
Trading Symbol HUAXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Mischler Financial Group Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [15]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000252319  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Penserra Shares
Trading Symbol PSFXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Penserra Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [16]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003926  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Premier Shares
Trading Symbol BUPXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Premier Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [17]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003929  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Private Client Shares
Trading Symbol BRPXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Private Client Shares
$34
0.68%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 34
Expense Ratio, Percent 0.68% [18]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.03%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.03%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003932  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Select Shares
Trading Symbol BFBXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Select Shares
$50
1.00%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 50
Expense Ratio, Percent 1.00% [19]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.71%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.71%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000237277  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Stern Brothers Shares
Trading Symbol SBIXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Stern Brothers Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [20]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000238342  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name Tigress Shares
Trading Symbol TIGXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Tigress Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [21]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000237291  
Shareholder Report [Line Items]  
Fund Name FedFund
Class Name WestCap Shares
Trading Symbol WSTXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about FedFund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
WestCap Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [22]
AssetsNet $ 191,671,446,613
Holdings Count | Holding 250
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$191,671,446,613
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
250
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.2%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
32.2
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
20.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003921  
Shareholder Report [Line Items]  
Fund Name TempCash
Class Name Institutional Shares
Trading Symbol TMCXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about TempCash (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Institutional Shares
$9
0.18%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.18% [23]
AssetsNet $ 24,558,863,826
Holdings Count | Holding 275
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$24,558,863,826
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
275
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.68%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.68%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
34.4%
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
30.1
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
19.5
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
10.5
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.7
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.9
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.4
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.3
C000003920  
Shareholder Report [Line Items]  
Fund Name TempCash
Class Name Capital Shares
Trading Symbol TPCXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about TempCash (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Capital Shares
$12
0.23%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 12
Expense Ratio, Percent 0.23% [24]
AssetsNet $ 24,558,863,826
Holdings Count | Holding 275
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$24,558,863,826
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
275
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.63%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.63%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
34.4%
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
30.1
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
19.5
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
10.5
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.7
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.9
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.4
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.3
C000003922  
Shareholder Report [Line Items]  
Fund Name TempCash
Class Name Dollar Shares
Trading Symbol TCDXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about TempCash (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Dollar Shares
$21
0.41%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 21
Expense Ratio, Percent 0.41% [25]
AssetsNet $ 24,558,863,826
Holdings Count | Holding 275
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$24,558,863,826
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
275
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.45%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.44%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
34.4%
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
30.1
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
19.5
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
10.5
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.7
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.9
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.4
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.3
C000240805  
Shareholder Report [Line Items]  
Fund Name TempCash
Class Name Great Pacific Shares
Trading Symbol GPCXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about TempCash (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Great Pacific Shares
$9
0.18%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.18% [26]
AssetsNet $ 24,558,863,826
Holdings Count | Holding 275
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$24,558,863,826
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
275
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.68%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.68%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
34.4%
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
30.1
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
19.5
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
10.5
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.7
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.9
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.4
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.3
C000003919  
Shareholder Report [Line Items]  
Fund Name TempCash
Class Name Premier Shares
Trading Symbol TCPXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about TempCash (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Premier Shares
$9
0.18%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.18% [27]
AssetsNet $ 24,558,863,826
Holdings Count | Holding 275
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$24,558,863,826
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
275
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.68%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.68%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
34.4%
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
30.1
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
19.5
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
10.5
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.7
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.9
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.4
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.3
C000003938  
Shareholder Report [Line Items]  
Fund Name T-Fund
Class Name Institutional Shares
Trading Symbol TSTXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about T-Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Institutional Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [28]
AssetsNet $ 123,626,153,470
Holdings Count | Holding 113
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$123,626,153,470
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
113
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
41.3
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003940  
Shareholder Report [Line Items]  
Fund Name T-Fund
Class Name Administration Shares
Trading Symbol BTAXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about T-Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Administration Shares
$14
0.27%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 14
Expense Ratio, Percent 0.27% [29]
AssetsNet $ 123,626,153,470
Holdings Count | Holding 113
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$123,626,153,470
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
113
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.44%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.44%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
41.3
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003936  
Shareholder Report [Line Items]  
Fund Name T-Fund
Class Name Capital Shares
Trading Symbol BCHXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about T-Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Capital Shares
$11
0.22%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 11
Expense Ratio, Percent 0.22% [30]
AssetsNet $ 123,626,153,470
Holdings Count | Holding 113
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$123,626,153,470
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
113
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.49%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.49%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
41.3
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003941  
Shareholder Report [Line Items]  
Fund Name T-Fund
Class Name Cash Management Shares
Trading Symbol BPTXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about T-Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Cash Management Shares
$33
0.67%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 33
Expense Ratio, Percent 0.67% [31]
AssetsNet $ 123,626,153,470
Holdings Count | Holding 113
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$123,626,153,470
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
113
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.04%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.04%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
41.3
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003937  
Shareholder Report [Line Items]  
Fund Name T-Fund
Class Name Cash Reserve Shares
Trading Symbol BTRXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about T-Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Cash Reserve Shares
$28
0.57%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 28
Expense Ratio, Percent 0.57% [32]
AssetsNet $ 123,626,153,470
Holdings Count | Holding 113
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$123,626,153,470
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
113
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.14%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.14%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
41.3
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003939  
Shareholder Report [Line Items]  
Fund Name T-Fund
Class Name Dollar Shares
Trading Symbol TFEXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about T-Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Dollar Shares
$21
0.42%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 21
Expense Ratio, Percent 0.42% [33]
AssetsNet $ 123,626,153,470
Holdings Count | Holding 113
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$123,626,153,470
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
113
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.29%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.29%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
41.3
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003935  
Shareholder Report [Line Items]  
Fund Name T-Fund
Class Name Premier Shares
Trading Symbol BEMXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about T-Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Premier Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [34]
AssetsNet $ 123,626,153,470
Holdings Count | Holding 113
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$123,626,153,470
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
113
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
41.3
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000060557  
Shareholder Report [Line Items]  
Fund Name T-Fund
Class Name Select Shares
Trading Symbol BSLXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about T-Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Select Shares
$50
1.00%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 50
Expense Ratio, Percent 1.00% [35]
AssetsNet $ 123,626,153,470
Holdings Count | Holding 113
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$123,626,153,470
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
113
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.71%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.71%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
53.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
41.3
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.0
C000003954  
Shareholder Report [Line Items]  
Fund Name Treasury Trust Fund
Class Name Institutional Shares
Trading Symbol TTTXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Treasury Trust Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Institutional Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [36]
AssetsNet $ 179,992,299,214
Holdings Count | Holding 59
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$179,992,299,214
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.53%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.55%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
100.4%
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.4)
C000003956  
Shareholder Report [Line Items]  
Fund Name Treasury Trust Fund
Class Name Administration Shares
Trading Symbol BITXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Treasury Trust Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Administration Shares
$13
0.27%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 13
Expense Ratio, Percent 0.27% [37]
AssetsNet $ 179,992,299,214
Holdings Count | Holding 59
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$179,992,299,214
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.43%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.45%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
100.4%
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.4)
C000003952  
Shareholder Report [Line Items]  
Fund Name Treasury Trust Fund
Class Name Capital Shares
Trading Symbol BUCXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Treasury Trust Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Capital Shares
$11
0.22%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 11
Expense Ratio, Percent 0.22% [38]
AssetsNet $ 179,992,299,214
Holdings Count | Holding 59
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$179,992,299,214
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.48%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.50%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
100.4%
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.4)
C000003957  
Shareholder Report [Line Items]  
Fund Name Treasury Trust Fund
Class Name Cash Management Shares
Trading Symbol BTCXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Treasury Trust Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Cash Management Shares
$33
0.67%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 33
Expense Ratio, Percent 0.67% [39]
AssetsNet $ 179,992,299,214
Holdings Count | Holding 59
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$179,992,299,214
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.03%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.05%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
100.4%
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.4)
C000003953  
Shareholder Report [Line Items]  
Fund Name Treasury Trust Fund
Class Name Cash Reserve Shares
Trading Symbol BTFXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Treasury Trust Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Cash Reserve Shares
$28
0.57%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 28
Expense Ratio, Percent 0.57% [40]
AssetsNet $ 179,992,299,214
Holdings Count | Holding 59
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$179,992,299,214
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.13%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.15%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
100.4%
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.4)
C000003955  
Shareholder Report [Line Items]  
Fund Name Treasury Trust Fund
Class Name Dollar Shares
Trading Symbol TTDXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Treasury Trust Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Dollar Shares
$21
0.42%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 21
Expense Ratio, Percent 0.42% [41]
AssetsNet $ 179,992,299,214
Holdings Count | Holding 59
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$179,992,299,214
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.28%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.30%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
100.4%
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.4)
C000060559  
Shareholder Report [Line Items]  
Fund Name Treasury Trust Fund
Class Name Select Shares
Trading Symbol TSLXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Treasury Trust Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Select Shares
$50
1.00%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 50
Expense Ratio, Percent 1.00% [42]
AssetsNet $ 179,992,299,214
Holdings Count | Holding 59
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$179,992,299,214
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.70%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.72%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
100.4%
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.4)
C000262010  
Shareholder Report [Line Items]  
Fund Name Treasury Trust Fund
Class Name DLT Shares
Trading Symbol DGLXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Treasury Trust Fund (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
DLT Shares
$9
0.17%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.17% [43]
AssetsNet $ 179,992,299,214
Holdings Count | Holding 59
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$179,992,299,214
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.54%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.55%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
100.4%
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.4)
C000003974  
Shareholder Report [Line Items]  
Fund Name MuniCash
Class Name Institutional Shares
Trading Symbol MCSXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about MuniCash (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7450.
Additional Information Phone Number (800) 441-7450
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)

Table Summary
Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Institutional Shares
$10
0.20%Footnote Reference(a)
FootnoteDescription
Footnote(a)
Annualized.
Expenses Paid, Amount $ 10
Expense Ratio, Percent 0.20% [44]
AssetsNet $ 3,953,089,896
Holdings Count | Holding 200
Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$3,953,089,896
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
200
Current seven-day yields as of April 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)
0
   7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.31%
   7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.31%
Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type
Percent of Net Assets
Variable Rate Demand Notes........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
94.4%
Closed-End Investment Companies........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
4.6
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.0
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