v3.26.1
N-2
12 Months Ended
Mar. 31, 2026
$ / shares
shares
Cover [Abstract]  
Entity Central Index Key 0001976685
Amendment Flag false
Entity Inv Company Type N-2
Document Type N-CSR
Entity Registrant Name Institutional Investment Strategy Fund
Founder Class  
General Description of Registrant [Abstract]  
NAV Per Share | $ / shares $ 12.02
Capital Stock, Long-Term Debt, and Other Securities [Abstract]  
Outstanding Security, Held [Shares] | shares 1,027,906
Investor Class  
General Description of Registrant [Abstract]  
NAV Per Share | $ / shares $ 12.04
Capital Stock, Long-Term Debt, and Other Securities [Abstract]  
Outstanding Security, Held [Shares] | shares 5,642