v3.26.1
State Street Federal Government Money Market Fund N-1A Cover
Sep. 04, 2026
Prospectus [Line Items]  
Document Type 485BPOS
Amendment Flag false
Registrant Name STATE STREET INSTITUTIONAL INVESTMENT TRUST
Entity Central Index Key 0001107414
Entity Investment Company Type N-1A
Document Period End Date Sep. 04, 2026
Prospectus Date Sep. 09, 2026