v3.26.1
Shareholder Report
 6 Months Ended
Apr. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name AB INSTITUTIONAL FUNDS INC
Entity Central Index Key 0001018592
Entity Investment Company Type N-1A
Document Period End Date Apr. 30, 2026
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
C000028538  
Shareholder Report [Line Items]  
Fund Name AB Global Real Estate Investment Fund II
Class Name Class I
Trading Symbol ARIIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the AB Global Real Estate Investment Fund II (the “Fund”) for the period of November 1, 2025 to April 30, 2026.
Additional Information [Text Block] Fund
Additional Information Phone Number (800) 227 4618
Additional Information Website https://www.abfunds.com/link/AB/ARIIX-S
Expenses [Text Block]

What were the Fund costs for the last six months?

(Based on a hypothetical $10,000 investment)

Table Summary
Class Name
Cost of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class I
$41
0.78%Footnote Reference*
Footnote Description
Footnote*
 Annualized
Expenses Paid, Amount $ 41
Expense Ratio, Percent 0.78% [1]
AssetsNet $ 189,293,556
Holdings Count | Holding 90
Advisory Fees Paid, Amount $ 500,231
InvestmentCompanyPortfolioTurnover 21.00%
Additional Fund Statistics [Text Block]

Key Fund Statistics

Table Summary
Net Assets
$189,293,556
# of Portfolio Holdings
90
Portfolio Turnover Rate
21%
Total Advisory Fees Paid (Net)
$500,231
Holdings [Text Block]

Country Breakdown (% of Net Assets)

Table Summary
United States
63.6%
Japan
9.3%
Australia
5.7%
Hong Kong
3.5%
United Kingdom
3.0%
Singapore
2.8%
Canada
2.0%
Switzerland
1.9%
France
1.7%
Germany
1.6%
Sweden
1.5%
Belgium
1.0%
Spain
0.7%
Israel
0.6%
Others
0.4%
Short-Term Investments
0.5%
Other assets less liabilities
0.2%
Total
100.0%

Sector Breakdown (% of Net Assets)

Table Summary
Equity Real Estate Investment Trusts (REITs)
80.9%
Real Estate Management & Development
16.1%
Health Care Equipment & Services
1.8%
Materials
0.5%
Short-Term Investments
0.5%
Other assets less liabilities
0.2%
Total
100.0%
Largest Holdings [Text Block]

10 Top Holdings

Table Summary
Company
U.S. $ Value
% of Net Assets
Welltower, Inc.
$13,947,360
7.4%
Prologis, Inc.
$12,724,282
6.7%
Equinix, Inc.
$9,698,908
5.1%
Digital Realty Trust, Inc.
$8,226,283
4.3%
Simon Property Group, Inc.
$6,841,600
3.6%
Extra Space Storage, Inc.
$5,946,905
3.1%
Mid-America Apartment Communities, Inc.
$4,120,842
2.2%
VICI Properties, Inc.
$4,080,992
2.2%
Goodman Group
$3,774,649
2.0%
Brixmor Property Group, Inc.
$3,592,565
1.9%
Total
$72,954,386
38.5%
Material Fund Change [Text Block]
[1] Annualized