v3.25.2
Shareholder Report
6 Months Ended
Jun. 30, 2025
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Vanguard Bond Index Funds
Entity Central Index Key 0000794105
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2025
C000226472  
Shareholder Report [Line Items]  
Fund Name Ultra-Short Bond ETF
Class Name ETF Shares
Trading Symbol VUSB
Security Exchange Name CboeBZX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Vanguard Ultra-Short Bond ETF (the "Fund") for the period of January 1, 2025, to June 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 https://personal1.vanguard.com/ngf-next-gen-form-webapp/fund-literature. You can also request this information by contacting us at 800-662-7447.
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
ETF Shares
$5
0.10%Footnote Reference1
FootnoteDescription
Footnote1
Annualized.
Expenses Paid, Amount $ 5
Expense Ratio, Percent 0.10% [1]
AssetsNet $ 5,356,000,000
Holdings Count | Holding 1,016
InvestmentCompanyPortfolioTurnover 39.00%
Additional Fund Statistics [Text Block]

Fund Statistics (as of June 30, 2025)

Fund Net Assets (in millions)
$5,356
Number of Portfolio Holdings
1,016
Portfolio Turnover Rate
39%
Holdings [Text Block]

Portfolio Composition % of Net Assets  (as of June 30, 2025)

Asset-Backed/Commercial Mortgage-Backed Securities
26.3%
Corporate Bonds
64.7%
Sovereign Bonds
2.5%
U.S. Government and Agency Obligations
1.6%
Other Assets and Liabilities—NetFootnote Reference
4.9%

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

Material Fund Change [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.