v3.25.4
Form N-1A Cover
Mar. 02, 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 Mar. 02, 2026
Prospectus Date Mar. 06, 2026