v3.26.1
Shareholder Report
 6 Months Ended
May 31, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Federated Hermes Investment Series Funds, Inc.
Entity Central Index Key 0000889388
Entity Investment Company Type N-1A
Document Period End Date May 31, 2026
Shareholder Report Annual or Semi-Annual Semi-Annual Shareholder Report
C000024768  
Shareholder Report [Line Items]  
Fund Name Federated Hermes Corporate Bond Fund
Class Name Class A Shares
Trading Symbol FDBAX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Federated Hermes Corporate Bond Fund (the "Fund") for the period of December 1, 2025 to May 31, 2026.
Additional Information [Text Block] You can find additional information at FederatedHermes.com/us/FundInformation. You can also request this information by contacting us at 1-800-341-7400, Option 4, or your financial advisor.
Additional Information Phone Number 1-800-341-7400
Additional Information Website FederatedHermes.com/us/FundInformation
Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Class Name
Costs of a $10,000 investment
Costs paid as an annualized percentage of a $10,000 investment
Class A Shares
$43
0.86%
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.86%
AssetsNet $ 972,536,107
Holdings Count | Holding 368
InvestmentCompanyPortfolioTurnover 5.00%
Additional Fund Statistics [Text Block]

Key Fund Statistics

  • Net Assets$972,536,107
  • Number of Investments368
  • Portfolio Turnover5%
Holdings [Text Block]

Top Security Types (% of Net Assets)Footnote Reference1

Group By Sector Chart
Table Summary
Value
Value
Preferred Stocks
0.0%Footnote Reference*
Mortgage-Backed Securities
0.0%Footnote Reference*
Common Stocks
0.0%Footnote Reference*
Municipal Bonds
0.0%Footnote Reference*
Cash Equivalents
0.4%
Corporate Debt Securities
98.4%
FootnoteDescription
Footnote1
Reflects the pro rata portfolio composition of underlying affiliated investment companies (other than an affiliated money market mutual fund) in which the Fund invested greater than 10% of its net assets as of the date specified above. Accordingly, the percentages of total net assets shown in the table will differ from those presented on the Portfolio of Investments.
Footnote*
Represents less than 0.1%.
Material Fund Change [Text Block]
C000024770  
Shareholder Report [Line Items]  
Fund Name Federated Hermes Corporate Bond Fund
Class Name Class C Shares
Trading Symbol FDBCX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Federated Hermes Corporate Bond Fund (the "Fund") for the period of December 1, 2025 to May 31, 2026.
Additional Information [Text Block] You can find additional information at FederatedHermes.com/us/FundInformation. You can also request this information by contacting us at 1-800-341-7400, Option 4, or your financial advisor.
Additional Information Phone Number 1-800-341-7400
Additional Information Website FederatedHermes.com/us/FundInformation
Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Class Name
Costs of a $10,000 investment
Costs paid as an annualized percentage of a $10,000 investment
Class C Shares
$83
1.67%
Expenses Paid, Amount $ 83
Expense Ratio, Percent 1.67%
AssetsNet $ 972,536,107
Holdings Count | Holding 368
InvestmentCompanyPortfolioTurnover 5.00%
Additional Fund Statistics [Text Block]

Key Fund Statistics

  • Net Assets$972,536,107
  • Number of Investments368
  • Portfolio Turnover5%
Holdings [Text Block]

Top Security Types (% of Net Assets)Footnote Reference1

Group By Sector Chart
Table Summary
Value
Value
Preferred Stocks
0.0%Footnote Reference*
Mortgage-Backed Securities
0.0%Footnote Reference*
Common Stocks
0.0%Footnote Reference*
Municipal Bonds
0.0%Footnote Reference*
Cash Equivalents
0.4%
Corporate Debt Securities
98.4%
FootnoteDescription
Footnote1
Reflects the pro rata portfolio composition of underlying affiliated investment companies (other than an affiliated money market mutual fund) in which the Fund invested greater than 10% of its net assets as of the date specified above. Accordingly, the percentages of total net assets shown in the table will differ from those presented on the Portfolio of Investments.
Footnote*
Represents less than 0.1%.
Material Fund Change [Text Block]
C000024771  
Shareholder Report [Line Items]  
Fund Name Federated Hermes Corporate Bond Fund
Class Name Class F Shares
Trading Symbol ISHIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Federated Hermes Corporate Bond Fund (the "Fund") for the period of December 1, 2025 to May 31, 2026.
Additional Information [Text Block] You can find additional information at FederatedHermes.com/us/FundInformation. You can also request this information by contacting us at 1-800-341-7400, Option 4, or your financial advisor.
Additional Information Phone Number 1-800-341-7400
Additional Information Website FederatedHermes.com/us/FundInformation
Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Class Name
Costs of a $10,000 investment
Costs paid as an annualized percentage of a $10,000 investment
Class F Shares
$43
0.86%
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.86%
AssetsNet $ 972,536,107
Holdings Count | Holding 368
InvestmentCompanyPortfolioTurnover 5.00%
Additional Fund Statistics [Text Block]

Key Fund Statistics

  • Net Assets$972,536,107
  • Number of Investments368
  • Portfolio Turnover5%
Holdings [Text Block]

Top Security Types (% of Net Assets)Footnote Reference1

Group By Sector Chart
Table Summary
Value
Value
Preferred Stocks
0.0%Footnote Reference*
Mortgage-Backed Securities
0.0%Footnote Reference*
Common Stocks
0.0%Footnote Reference*
Municipal Bonds
0.0%Footnote Reference*
Cash Equivalents
0.4%
Corporate Debt Securities
98.4%
FootnoteDescription
Footnote1
Reflects the pro rata portfolio composition of underlying affiliated investment companies (other than an affiliated money market mutual fund) in which the Fund invested greater than 10% of its net assets as of the date specified above. Accordingly, the percentages of total net assets shown in the table will differ from those presented on the Portfolio of Investments.
Footnote*
Represents less than 0.1%.
Material Fund Change [Text Block]
C000062220  
Shareholder Report [Line Items]  
Fund Name Federated Hermes Corporate Bond Fund
Class Name Institutional Shares
Trading Symbol FDBIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Federated Hermes Corporate Bond Fund (the "Fund") for the period of December 1, 2025 to May 31, 2026.
Additional Information [Text Block] You can find additional information at FederatedHermes.com/us/FundInformation. You can also request this information by contacting us at 1-800-341-7400, Option 4, or your financial advisor.
Additional Information Phone Number 1-800-341-7400
Additional Information Website FederatedHermes.com/us/FundInformation
Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Class Name
Costs of a $10,000 investment
Costs paid as an annualized percentage of a $10,000 investment
Institutional Shares
$31
0.61%
Expenses Paid, Amount $ 31
Expense Ratio, Percent 0.61%
AssetsNet $ 972,536,107
Holdings Count | Holding 368
InvestmentCompanyPortfolioTurnover 5.00%
Additional Fund Statistics [Text Block]

Key Fund Statistics

  • Net Assets$972,536,107
  • Number of Investments368
  • Portfolio Turnover5%
Holdings [Text Block]

Top Security Types (% of Net Assets)Footnote Reference1

Group By Sector Chart
Table Summary
Value
Value
Preferred Stocks
0.0%Footnote Reference*
Mortgage-Backed Securities
0.0%Footnote Reference*
Common Stocks
0.0%Footnote Reference*
Municipal Bonds
0.0%Footnote Reference*
Cash Equivalents
0.4%
Corporate Debt Securities
98.4%
FootnoteDescription
Footnote1
Reflects the pro rata portfolio composition of underlying affiliated investment companies (other than an affiliated money market mutual fund) in which the Fund invested greater than 10% of its net assets as of the date specified above. Accordingly, the percentages of total net assets shown in the table will differ from those presented on the Portfolio of Investments.
Footnote*
Represents less than 0.1%.
Material Fund Change [Text Block]
C000173769  
Shareholder Report [Line Items]  
Fund Name Federated Hermes Corporate Bond Fund
Class Name Class R6 Shares
Trading Symbol FDBLX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Federated Hermes Corporate Bond Fund (the "Fund") for the period of December 1, 2025 to May 31, 2026.
Additional Information [Text Block] You can find additional information at FederatedHermes.com/us/FundInformation. You can also request this information by contacting us at 1-800-341-7400, Option 4, or your financial advisor.
Additional Information Phone Number 1-800-341-7400
Additional Information Website FederatedHermes.com/us/FundInformation
Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Class Name
Costs of a $10,000 investment
Costs paid as an annualized percentage of a $10,000 investment
Class R6 Shares
$29
0.59%
Expenses Paid, Amount $ 29
Expense Ratio, Percent 0.59%
AssetsNet $ 972,536,107
Holdings Count | Holding 368
InvestmentCompanyPortfolioTurnover 5.00%
Additional Fund Statistics [Text Block]

Key Fund Statistics

  • Net Assets$972,536,107
  • Number of Investments368
  • Portfolio Turnover5%
Holdings [Text Block]

Top Security Types (% of Net Assets)Footnote Reference1

Group By Sector Chart
Table Summary
Value
Value
Preferred Stocks
0.0%Footnote Reference*
Mortgage-Backed Securities
0.0%Footnote Reference*
Common Stocks
0.0%Footnote Reference*
Municipal Bonds
0.0%Footnote Reference*
Cash Equivalents
0.4%
Corporate Debt Securities
98.4%
FootnoteDescription
Footnote1
Reflects the pro rata portfolio composition of underlying affiliated investment companies (other than an affiliated money market mutual fund) in which the Fund invested greater than 10% of its net assets as of the date specified above. Accordingly, the percentages of total net assets shown in the table will differ from those presented on the Portfolio of Investments.
Footnote*
Represents less than 0.1%.
Material Fund Change [Text Block]