v3.26.1
Shareholder Report
 6 Months Ended 12 Months Ended
Jun. 30, 2026
USD ($)
Holding
Dec. 31, 2025
Shareholder Report [Line Items]    
Document Type N-CSRS  
Amendment Flag false  
Registrant Name Vanguard Montgomery Funds  
Entity Central Index Key 0001409957  
Entity Investment Company Type N-1A  
Document Period End Date Jun. 30, 2026  
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report  
C000054090    
Shareholder Report [Line Items]    
Fund Name Market Neutral Fund  
Class Name Investor Shares  
Trading Symbol VMNFX  
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Vanguard Market Neutral 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 <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;"> 800-662-7447</span>  
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
Investor Shares
$127
2.39%Footnote Reference1
FootnoteDescription
Footnote1
Annualized.
  
Expenses Paid, Amount $ 127  
Expense Ratio, Percent [1] 2.39%  
Material Change Date   Dec. 31, 2025
AssetsNet $ 601,000,000  
Holdings Count | Holding 615  
InvestmentCompanyPortfolioTurnover 52.00%  
Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2026)

Table Summary
Fund Net Assets (in millions)
$601
Number of Portfolio Holdings
615
Portfolio Turnover Rate
52%
  
Holdings [Text Block]

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

Table Summary
Sector
Long Portfolio
Short Portfolio
Communication Services
3.2%
3.8%
Consumer Discretionary
13.4%
13.4%
Consumer Staples
1.9%
1.9%
Energy
4.0%
4.2%
Financials
19.6%
18.8%
Health Care
12.1%
12.1%
Industrials
14.0%
14.0%
Information Technology
12.2%
11.1%
Materials
4.2%
4.5%
Real Estate
8.6%
8.6%
Utilities
3.0%
2.9%
Other Assets and Liabilities—Net
3.8%
4.7%

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 Portfolio 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 Portfolio Management, LLC.

  
Summary of Change Legend [Text Block]

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.

  
Updated Prospectus Phone Number 800-662-7447  
Updated Prospectus Web Address https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature  
C000054091    
Shareholder Report [Line Items]    
Fund Name Market Neutral Fund  
Class Name Institutional Shares  
Trading Symbol VMNIX  
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Vanguard Market Neutral 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 <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;"> 800-662-7447</span>  
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
$133
2.51%Footnote Reference1
FootnoteDescription
Footnote1
Annualized.
  
Expenses Paid, Amount $ 133  
Expense Ratio, Percent [2] 2.51%  
Material Change Date   Dec. 31, 2025
AssetsNet $ 601,000,000  
Holdings Count | Holding 615  
InvestmentCompanyPortfolioTurnover 52.00%  
Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2026)

Table Summary
Fund Net Assets (in millions)
$601
Number of Portfolio Holdings
615
Portfolio Turnover Rate
52%
  
Holdings [Text Block]

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

Table Summary
Sector
Long Portfolio
Short Portfolio
Communication Services
3.2%
3.8%
Consumer Discretionary
13.4%
13.4%
Consumer Staples
1.9%
1.9%
Energy
4.0%
4.2%
Financials
19.6%
18.8%
Health Care
12.1%
12.1%
Industrials
14.0%
14.0%
Information Technology
12.2%
11.1%
Materials
4.2%
4.5%
Real Estate
8.6%
8.6%
Utilities
3.0%
2.9%
Other Assets and Liabilities—Net
3.8%
4.7%

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 Portfolio 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 Portfolio Management, LLC.

  
Summary of Change Legend [Text Block]

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.

  
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.