This semi-annual shareholder report contains important information about BlackRock Liquid Federal Trust Fund (the “Fund”) for the period of November 1, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[1]

AssetsNet

$ 6,550,383,444

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$6,550,383,444
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	95
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.18%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.18%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	70.0%
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	33.0
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	(3.0)

C000003942

Shareholder Report [Line Items]

Fund Name

BlackRock Liquid Federal Trust 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 Liquid Federal Trust Fund (the “Fund”) for the period of November 1, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 14

Expense Ratio, Percent

0.27%

^[2]

AssetsNet

$ 6,550,383,444

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$6,550,383,444
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	95
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.08%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.08%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	70.0%
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	33.0
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	(3.0)

C000003943

Shareholder Report [Line Items]

Fund Name

BlackRock Liquid Federal Trust 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 Liquid Federal Trust Fund (the “Fund”) for the period of November 1, 2024 to April 30, 2025.

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)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Cash Management Shares	$34	0.67%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 34

Expense Ratio, Percent

0.67%

^[3]

AssetsNet

$ 6,550,383,444

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$6,550,383,444
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	95
Current seven-day yields as of April 30, 2025 (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

Asset Type	Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	70.0%
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	33.0
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	(3.0)

C000003949

Shareholder Report [Line Items]

Fund Name

BlackRock Liquid Federal Trust 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 Liquid Federal Trust Fund (the “Fund”) for the period of November 1, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 21

Expense Ratio, Percent

0.42%

^[4]

AssetsNet

$ 6,550,383,444

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$6,550,383,444
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	95
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.93%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.93%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	70.0%
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	33.0
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	(3.0)

C000231604

Shareholder Report [Line Items]

Fund Name

BlackRock Liquid Federal Trust 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 Liquid Federal Trust Fund (the “Fund”) for the period of November 1, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[5]

AssetsNet

$ 6,550,383,444

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$6,550,383,444
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	95
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.18%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.18%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	70.0%
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	33.0
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	(3.0)

C000237278

Shareholder Report [Line Items]

Fund Name

BlackRock Liquid Federal Trust 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 Liquid Federal Trust Fund (the “Fund”) for the period of November 1, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[6]

AssetsNet

$ 6,550,383,444

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$6,550,383,444
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	95
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.18%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.18%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	70.0%
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	33.0
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	(3.0)

C000238343

Shareholder Report [Line Items]

Fund Name

BlackRock Liquid Federal Trust 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 Liquid Federal Trust Fund (the “Fund”) for the period of November 1, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[7]

AssetsNet

$ 6,550,383,444

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$6,550,383,444
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	95
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.18%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.18%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	70.0%
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	33.0
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	(3.0)

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[8]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 14

Expense Ratio, Percent

0.27%

^[9]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.12%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.12%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 11

Expense Ratio, Percent

0.22%

^[10]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.17%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.17%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 33

Expense Ratio, Percent

0.67%

^[11]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.73%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.73%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Cash Reserve Shares	$29	0.57%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 29

Expense Ratio, Percent

0.57%

^[12]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.82%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.82%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 21

Expense Ratio, Percent

0.42%

^[13]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.97%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.97%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[14]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[15]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[16]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[17]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 34

Expense Ratio, Percent

0.68%

^[18]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.71%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.71%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 50

Expense Ratio, Percent

1.00%

^[19]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.39%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.39%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[20]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[21]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[22]

AssetsNet

$ 168,587,818,648

Holdings Count | Holding

190

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$168,587,818,648
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	190
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.22%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	47.3%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	37.1
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.18%

^[23]

AssetsNet

$ 22,151,235,110

Holdings Count | Holding

248

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$22,151,235,110
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	248
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.33%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.33%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	30.9%
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	22.8
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	21.3
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	20.0
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.0
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.5
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.4
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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 April 14, 2025 to April 30, 2025.

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 period?

(based on a hypothetical $10,000 investment)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Capital Shares	$1^{Footnote Reference(a)}	0.18%^{Footnote Reference(b)}

Footnote	Description
Footnote^(a)	The Capital Shares commenced operations during the reporting period. Expenses for a full reporting period would be higher than the amount shown.
Footnote^(b)	Annualized.

Expenses Paid, Amount

$ 1

^[24]

Expense Ratio, Percent

0.18%

^[25]

AssetsNet

$ 22,151,235,110

Holdings Count | Holding

248

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$22,151,235,110
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	248
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.34%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.34%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	30.9%
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	22.8
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	21.3
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	20.0
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.0
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.5
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.4
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Dollar Shares	$14	0.28%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 14

Expense Ratio, Percent

0.28%

^[26]

AssetsNet

$ 22,151,235,110

Holdings Count | Holding

248

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$22,151,235,110
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	248
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.20%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.20%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	30.9%
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	22.8
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	21.3
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	20.0
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.0
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.5
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.4
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.18%

^[27]

AssetsNet

$ 22,151,235,110

Holdings Count | Holding

248

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$22,151,235,110
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	248
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.33%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.33%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	30.9%
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	22.8
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	21.3
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	20.0
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.0
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.5
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.4
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.18%

^[28]

AssetsNet

$ 22,151,235,110

Holdings Count | Holding

248

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$22,151,235,110
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	248
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.33%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.33%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Commercial Paper........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	30.9%
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	22.8
Certificates of Deposit........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	21.3
Time Deposits........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	20.0
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.0
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.5
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.4
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[29]

AssetsNet

$ 112,316,303,127

Holdings Count | Holding

109

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$112,316,303,127
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	109
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.21%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.21%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	51.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	45.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 14

Expense Ratio, Percent

0.27%

^[30]

AssetsNet

$ 112,316,303,127

Holdings Count | Holding

109

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$112,316,303,127
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	109
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.11%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.11%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	51.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	45.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 11

Expense Ratio, Percent

0.22%

^[31]

AssetsNet

$ 112,316,303,127

Holdings Count | Holding

109

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$112,316,303,127
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	109
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.16%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.16%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	51.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	45.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Cash Management Shares	$34	0.67%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 34

Expense Ratio, Percent

0.67%

^[32]

AssetsNet

$ 112,316,303,127

Holdings Count | Holding

109

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$112,316,303,127
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	109
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.72%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.72%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	51.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	45.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 28

Expense Ratio, Percent

0.57%

^[33]

AssetsNet

$ 112,316,303,127

Holdings Count | Holding

109

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$112,316,303,127
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	109
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.82%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.82%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	51.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	45.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 21

Expense Ratio, Percent

0.42%

^[34]

AssetsNet

$ 112,316,303,127

Holdings Count | Holding

109

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$112,316,303,127
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	109
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.96%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.96%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	51.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	45.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[35]

AssetsNet

$ 112,316,303,127

Holdings Count | Holding

109

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$112,316,303,127
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	109
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.21%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.21%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	51.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	45.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 50

Expense Ratio, Percent

1.00%

^[36]

AssetsNet

$ 112,316,303,127

Holdings Count | Holding

109

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$112,316,303,127
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	109
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.38%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.38%

Holdings [Text Block]

Portfolio composition

Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	51.7%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	45.2
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.1

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 9

Expense Ratio, Percent

0.17%

^[37]

AssetsNet

$ 149,640,686,804

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$149,640,686,804
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	48
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.17%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.17%

Holdings [Text Block]

Portfolio composition

Asset Type

Percent of
Net Assets

U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

106.8%

Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

(6.8)

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 13

Expense Ratio, Percent

0.27%

^[38]

AssetsNet

$ 149,640,686,804

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$149,640,686,804
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	48
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.07%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.07%

Holdings [Text Block]

Portfolio composition

Asset Type

Percent of
Net Assets

U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

106.8%

Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

(6.8)

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 11

Expense Ratio, Percent

0.22%

^[39]

AssetsNet

$ 149,640,686,804

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$149,640,686,804
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	48
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.12%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.12%

Holdings [Text Block]

Portfolio composition

Asset Type

Percent of
Net Assets

U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

106.8%

Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

(6.8)

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, 2024 to April 30, 2025.

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)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Cash Management Shares	$34	0.67%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 34

Expense Ratio, Percent

0.67%

^[40]

AssetsNet

$ 149,640,686,804

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$149,640,686,804
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	48
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.67%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.67%

Holdings [Text Block]

Portfolio composition

Asset Type

Percent of
Net Assets

U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

106.8%

Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

(6.8)

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, 2024 to April 30, 2025.

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)

Class name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Cash Reserve Shares	$29	0.57%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 29

Expense Ratio, Percent

0.57%

^[41]

AssetsNet

$ 149,640,686,804

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$149,640,686,804
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	48
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.77%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.77%

Holdings [Text Block]

Portfolio composition

Asset Type

Percent of
Net Assets

U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

106.8%

Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

(6.8)

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 21

Expense Ratio, Percent

0.41%

^[42]

AssetsNet

$ 149,640,686,804

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$149,640,686,804
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	48
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.93%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.93%

Holdings [Text Block]

Portfolio composition

Asset Type

Percent of
Net Assets

U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

106.8%

Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

(6.8)

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 50

Expense Ratio, Percent

1.00%

^[43]

AssetsNet

$ 149,640,686,804

Holdings Count | Holding

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$149,640,686,804
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	48
Current seven-day yields as of April 30, 2025 (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........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.34%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.34%

Holdings [Text Block]

Portfolio composition

Asset Type

Percent of
Net Assets

U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

106.8%

Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

(6.8)

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, 2024 to April 30, 2025.

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)

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)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 10

Expense Ratio, Percent

0.20%

^[44]

AssetsNet

$ 3,899,455,799

Holdings Count | Holding

179

Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$3,899,455,799
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	179
Current seven-day yields as of April 30, 2025 (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

Asset Type	Percent of Net Assets
Variable Rate Demand Notes........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	92.5%
Closed-End Investment Companies........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.7
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.8

[1]	Annualized.
[2]	Annualized.
[3]	Annualized.
[4]	Annualized.
[5]	Annualized.
[6]	Annualized.
[7]	Annualized.
[8]	Annualized.
[9]	Annualized.
[10]	Annualized.
[11]	Annualized.
[12]	Annualized.
[13]	Annualized.
[14]	Annualized.
[15]	Annualized.
[16]	Annualized.
[17]	Annualized.
[18]	Annualized.
[19]	Annualized.
[20]	Annualized.
[21]	Annualized.
[22]	Annualized.
[23]	Annualized.
[24]	The Capital Shares commenced operations during the reporting period. Expenses for a full reporting period would be higher than the amount shown.
[25]	Annualized.
[26]	Annualized.
[27]	Annualized.
[28]	Annualized.
[29]	Annualized.
[30]	Annualized.
[31]	Annualized.
[32]	Annualized.
[33]	Annualized.
[34]	Annualized.
[35]	Annualized.
[36]	Annualized.
[37]	Annualized.
[38]	Annualized.
[39]	Annualized.
[40]	Annualized.
[41]	Annualized.
[42]	Annualized.
[43]	Annualized.
[44]	Annualized.