v3.26.1
Vanguard Total Bond Market II Index Fund N-1A Cover
Dec. 31, 2025
Prospectus [Line Items]  
Document Type 485BPOS
Amendment Flag false
Registrant Name Vanguard Bond Index Funds
Entity Central Index Key 0000794105
Entity Investment Company Type N-1A
Document Period End Date Dec. 31, 2025
Prospectus Date Apr. 28, 2026