v3.26.1
Shareholder Report
 6 Months Ended
Jun. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Vanguard Valley Forge Funds
Entity Central Index Key 0000889519
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
C000007056 [Member]  
Shareholder Report [Line Items]  
Fund Name Vanguard Balanced Index Fund
Class Name Institutional Shares
Trading Symbol VBAIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Vanguard Balanced Index Fund (the "Fund") for the period of January 1, 2026, to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at 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 800-662-7447
Additional Information Website https://personal1.vanguard.com/ngf‑next‑gen‑form‑webapp/fund‑literature
Expenses [Text Block]
What were the Fund costs for the last six months?
(based on a hypothetical $10,000 investment)
Share Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Institutional Shares $2 0.04%1
​1
Annualized.
Expenses Paid, Amount $ 2
Expense Ratio, Percent 0.04% [1]
Net Assets $ 63,699,000,000
Holdings Count | Holding 16,316
Investment Company Portfolio Turnover 21.00%
Additional Fund Statistics [Text Block]
Fund Statistics
(as of June 30, 2026)
Fund Net Assets
(in millions)		 $63,699
Number of Portfolio Holdings 16,316
Portfolio Turnover Rate 21%
Holdings [Text Block]
Portfolio Composition % of Net Assets
(as of June 30, 2026)
Asset-Backed/Commercial Mortgage-Backed Securities 0.8%
Common Stocks 61.2%
Corporate Bonds 9.7%
Rights 0.0%
Sovereign Bonds 1.3%
Taxable Municipal Bonds 0.2%
U.S. Government and Agency Obligations 26.3%
Other Assets and Liabilities—Net 0.5%
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.
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
C000007055 [Member]  
Shareholder Report [Line Items]  
Fund Name Vanguard Balanced Index Fund
Class Name Admiral™ Shares
Trading Symbol VBIAX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Vanguard Balanced Index Fund (the "Fund") for the period of January 1, 2026, to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at 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 800-662-7447
Additional Information Website https://personal1.vanguard.com/ngf‑next‑gen‑form‑webapp/fund‑literature
Expenses [Text Block]
What were the Fund costs for the last six months?
(based on a hypothetical $10,000 investment)
Share Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Admiral Shares $4 0.07%1
​1
Annualized.
Expenses Paid, Amount $ 4
Expense Ratio, Percent 0.07% [2]
Net Assets $ 63,699,000,000
Holdings Count | Holding 16,316
Investment Company Portfolio Turnover 21.00%
Additional Fund Statistics [Text Block]
Fund Statistics
(as of June 30, 2026)
Fund Net Assets
(in millions)		 $63,699
Number of Portfolio Holdings 16,316
Portfolio Turnover Rate 21%
Holdings [Text Block]
Portfolio Composition % of Net Assets
(as of June 30, 2026)
Asset-Backed/Commercial Mortgage-Backed Securities 0.8%
Common Stocks 61.2%
Corporate Bonds 9.7%
Rights 0.0%
Sovereign Bonds 1.3%
Taxable Municipal Bonds 0.2%
U.S. Government and Agency Obligations 26.3%
Other Assets and Liabilities—Net 0.5%
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.
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
C000007054 [Member]  
Shareholder Report [Line Items]  
Fund Name Vanguard Balanced Index Fund
Class Name Investor Shares
Trading Symbol VBINX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Vanguard Balanced Index Fund (the "Fund") for the period of January 1, 2026, to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at 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 800-662-7447
Additional Information Website https://personal1.vanguard.com/ngf‑next‑gen‑form‑webapp/fund‑literature
Expenses [Text Block]
What were the Fund costs for the last six months?
(based on a hypothetical $10,000 investment)
Share Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Investor Shares $9 0.18%1
​1
Annualized.
Expenses Paid, Amount $ 9
Expense Ratio, Percent 0.18% [3]
Net Assets $ 63,699,000,000
Holdings Count | Holding 16,316
Investment Company Portfolio Turnover 21.00%
Additional Fund Statistics [Text Block]
Fund Statistics
(as of June 30, 2026)
Fund Net Assets
(in millions)		 $63,699
Number of Portfolio Holdings 16,316
Portfolio Turnover Rate 21%
Holdings [Text Block]
Portfolio Composition % of Net Assets
(as of June 30, 2026)
Asset-Backed/Commercial Mortgage-Backed Securities 0.8%
Common Stocks 61.2%
Corporate Bonds 9.7%
Rights 0.0%
Sovereign Bonds 1.3%
Taxable Municipal Bonds 0.2%
U.S. Government and Agency Obligations 26.3%
Other Assets and Liabilities—Net 0.5%
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.
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.
[3]
Annualized.