v3.26.1
Siebert Williams Shank Shares [Member] N-1A Cover
Nov. 30, 2025
Prospectus [Line Items]  
Document Type 485BPOS
Amendment Flag false
Registrant Name NORTHERN INSTITUTIONAL FUNDS
Entity Central Index Key 0000710124
Entity Investment Company Type N-1A
Document Period End Date Nov. 30, 2025
Prospectus Date Apr. 01, 2026