This semi-annual shareholder report contains important information about Vanguard Institutional Index Fund (the "Fund") for the period of January 1, 2026, to June 30, 2026.

Additional Information [Text Block]

You can find additional information about the Fund at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.

Material Fund Change Notice [Text Block]

The report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

Additional Information Website

<span style="white-space: nowrap; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto;"><span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: collapse;"><span style="text-decoration: underline; box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 10.6667px; font-weight: 400; grid-area: auto; line-height: 16px; margin: 0px; overflow: visible; text-align: left; text-align-last: auto; white-space-collapse: collapse;">https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature</span></span></span>

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Share Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Institutional Shares	$2	0.035%^{Footnote Reference1}

Footnote	Description
Footnote¹	Annualized.

Expenses Paid, Amount

$ 2

Expense Ratio, Percent

^[1]

0.035%

Material Change Date

Dec. 31, 2025

AssetsNet

$ 349,726,000,000

Holdings Count | Holding

516

InvestmentCompanyPortfolioTurnover

1.00%

Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2026)

Table Summary
Fund Net Assets (in millions)	$349,726
Number of Portfolio Holdings	516
Portfolio Turnover Rate	1%

Holdings [Text Block]

Portfolio Composition % of Net Assets (as of June 30, 2026)

Table Summary
Communication Services	9.7%
Consumer Discretionary	9.3%
Consumer Staples	4.6%
Energy	3.0%
Financials	11.6%
Health Care	8.9%
Industrials	8.9%
Information Technology	38.0%
Materials	1.8%
Real Estate	1.8%
Utilities	2.2%
Other Assets and Liabilities—Net	0.2%

This table reflects the Fund's investments, including short-term investments, derivatives and other assets and liabilities.

Material Fund Change [Text Block]

How has the Fund changed?

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

This is a summary of certain changes to the Fund since December 31, 2025. For more complete information, you may review the Fund’s prospectus, at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature or upon request at 800-662-7447.

Material Fund Change Adviser [Text Block]

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

800-662-7447

Updated Prospectus Web Address

https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature

C000007826

Shareholder Report [Line Items]

Fund Name

Institutional Index Fund

Class Name

Institutional Plus Shares

Trading Symbol

VIIIX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Vanguard Institutional Index Fund (the "Fund") for the period of January 1, 2026, to June 30, 2026.

Additional Information [Text Block]

You can find additional information about the Fund at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.

Material Fund Change Notice [Text Block]

The report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

Additional Information Website

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Share Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Institutional Plus Shares	$1	0.02%^{Footnote Reference1}

Footnote	Description
Footnote¹	Annualized.

Expenses Paid, Amount

$ 1

Expense Ratio, Percent

^[2]

0.02%

Material Change Date

Dec. 31, 2025

AssetsNet

$ 349,726,000,000

Holdings Count | Holding

516

InvestmentCompanyPortfolioTurnover

1.00%

Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2026)

Table Summary
Fund Net Assets (in millions)	$349,726
Number of Portfolio Holdings	516
Portfolio Turnover Rate	1%

Holdings [Text Block]

Portfolio Composition % of Net Assets (as of June 30, 2026)

Table Summary
Communication Services	9.7%
Consumer Discretionary	9.3%
Consumer Staples	4.6%
Energy	3.0%
Financials	11.6%
Health Care	8.9%
Industrials	8.9%
Information Technology	38.0%
Materials	1.8%
Real Estate	1.8%
Utilities	2.2%
Other Assets and Liabilities—Net	0.2%

This table reflects the Fund's investments, including short-term investments, derivatives and other assets and liabilities.

Material Fund Change [Text Block]

How has the Fund changed?

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Material Fund Change Adviser [Text Block]

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

800-662-7447

Updated Prospectus Web Address

https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature

C000007828

Shareholder Report [Line Items]

Fund Name

Morningstar Institutional Total Stock Market Index Fund

Class Name

Institutional Shares

Trading Symbol

VITNX

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Vanguard Morningstar Institutional Total Stock Market Index Fund (the "Fund") (formerly known as Vanguard Institutional Total Stock Market Index Fund) for the period of January 1, 2026, to June 30, 2026.

Additional Information [Text Block]

You can find additional information about the Fund at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.

Material Fund Change Notice [Text Block]

The report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

Additional Information Website

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Share Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Institutional Shares	$2	0.03%^{Footnote Reference1}

Footnote	Description
Footnote¹	Annualized.

Expenses Paid, Amount

$ 2

Expense Ratio, Percent

^[3]

0.03%

Material Change Date

Dec. 31, 2025

AssetsNet

$ 34,653,000,000

Holdings Count | Holding

3,183

InvestmentCompanyPortfolioTurnover

3.00%

Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2026)

Table Summary
Fund Net Assets (in millions)	$34,653
Number of Portfolio Holdings	3,183
Portfolio Turnover Rate	3%

Holdings [Text Block]

Portfolio Composition % of Net Assets (as of June 30, 2026)

Table Summary
Basic Materials	1.6%
Consumer Discretionary	12.3%
Consumer Staples	3.3%
Energy	3.2%
Financials	9.9%
Health Care	9.2%
Industrials	12.4%
Other	0.0%
Real Estate	2.2%
Technology	41.0%
Telecommunications	2.1%
Utilities	2.5%
Other Assets and Liabilities—Net	0.3%

This table reflects the Fund's investments, including short-term investments, derivatives and other assets and liabilities.

Material Fund Change [Text Block]

How has the Fund changed?

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Material Fund Change Adviser [Text Block]

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

800-662-7447

Updated Prospectus Web Address

https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature

C000007829

Shareholder Report [Line Items]

Fund Name

Morningstar Institutional Total Stock Market Index Fund

Class Name

Institutional Plus Shares

Trading Symbol

VITPX

Annual or Semi-Annual Statement [Text Block]

Additional Information [Text Block]

You can find additional information about the Fund at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.

Material Fund Change Notice [Text Block]

The report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

Additional Information Website

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Share Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
Institutional Plus Shares	$1	0.02%^{Footnote Reference1}

Footnote	Description
Footnote¹	Annualized.

Expenses Paid, Amount

$ 1

Expense Ratio, Percent

^[4]

0.02%

Material Change Date

Dec. 31, 2025

AssetsNet

$ 34,653,000,000

Holdings Count | Holding

3,183

InvestmentCompanyPortfolioTurnover

3.00%

Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2026)

Table Summary
Fund Net Assets (in millions)	$34,653
Number of Portfolio Holdings	3,183
Portfolio Turnover Rate	3%

Holdings [Text Block]

Portfolio Composition % of Net Assets (as of June 30, 2026)

Table Summary
Basic Materials	1.6%
Consumer Discretionary	12.3%
Consumer Staples	3.3%
Energy	3.2%
Financials	9.9%
Health Care	9.2%
Industrials	12.4%
Other	0.0%
Real Estate	2.2%
Technology	41.0%
Telecommunications	2.1%
Utilities	2.5%
Other Assets and Liabilities—Net	0.3%

This table reflects the Fund's investments, including short-term investments, derivatives and other assets and liabilities.

Material Fund Change [Text Block]

How has the Fund changed?

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Material Fund Change Adviser [Text Block]

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

800-662-7447

Updated Prospectus Web Address

https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature

C000257083

Shareholder Report [Line Items]

Fund Name

0-3 Month Treasury Bill ETF

Class Name

ETF Shares

Trading Symbol

VBIL

Security Exchange Name

NASDAQ

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Vanguard 0-3 Month Treasury Bill ETF (the "Fund") for the period of January 1, 2026, to June 30, 2026.

Additional Information [Text Block]

You can find additional information about the Fund at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.

Material Fund Change Notice [Text Block]

The report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

Additional Information Website

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Share Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
ETF Shares	$3	0.06%^{Footnote Reference1}

Footnote	Description
Footnote¹	Annualized.

Expenses Paid, Amount

$ 3

Expense Ratio, Percent

^[5]

0.06%

Material Change Date

Dec. 31, 2025

AssetsNet

$ 9,392,000,000

Holdings Count | Holding

InvestmentCompanyPortfolioTurnover

0.00%

Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2026)

Table Summary
Fund Net Assets (in millions)	$9,392
Number of Portfolio Holdings	27
Portfolio Turnover Rate	0%

Holdings [Text Block]

Portfolio Composition % of Net Assets (as of June 30, 2026)

Table Summary
U.S. Government and Agency Obligations	99.9%
Other Assets and Liabilities—Net^{Footnote Reference}	0.1%

This table reflects the Fund's investments, including short-term investments and other assets and liabilities.

Material Fund Change [Text Block]

How has the Fund changed?

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Material Fund Change Adviser [Text Block]

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

800-662-7447

Updated Prospectus Web Address

https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature

C000257084

Shareholder Report [Line Items]

Fund Name

Ultra-Short Treasury ETF

Class Name

ETF Shares

Trading Symbol

VGUS

Security Exchange Name

NASDAQ

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about Vanguard Ultra-Short Treasury ETF (the "Fund") for the period of January 1, 2026, to June 30, 2026.

Additional Information [Text Block]

You can find additional information about the Fund at https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.

Material Fund Change Notice [Text Block]

The report describes changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

Additional Information Website

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Share Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
ETF Shares	$4	0.07%^{Footnote Reference1}

Footnote	Description
Footnote¹	Annualized.

Expenses Paid, Amount

$ 4

Expense Ratio, Percent

^[6]

0.07%

Material Change Date

Dec. 31, 2025

AssetsNet

$ 1,019,000,000

Holdings Count | Holding

InvestmentCompanyPortfolioTurnover

15.00%

Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2026)

Table Summary
Fund Net Assets (in millions)	$1,019
Number of Portfolio Holdings	90
Portfolio Turnover Rate	15%

Holdings [Text Block]

Portfolio Composition % of Net Assets (as of June 30, 2026)

Table Summary
U.S. Government and Agency Obligations	99.5%
Other Assets and Liabilities—Net^{Footnote Reference}	0.5%

This table reflects the Fund's investments, including short-term investments and other assets and liabilities.

Material Fund Change [Text Block]

How has the Fund changed?

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Material Fund Change Adviser [Text Block]

Effective January 12, 2026, The Vanguard Group, Inc. exercises portfolio management responsibilities for the fund through its wholly-owned subsidiary, Vanguard Capital Management, LLC.

Summary of Change Legend [Text Block]

Updated Prospectus Phone Number

800-662-7447

Updated Prospectus Web Address

https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature

[1]	Annualized.
[2]	Annualized.
[3]	Annualized.
[4]	Annualized.
[5]	Annualized.
[6]	Annualized.