v3.26.1
Shareholder Report
 6 Months Ended
Jun. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS/A
Amendment Flag false
Registrant Name BNY Mellon Investment Funds III
Entity Central Index Key 0000053808
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
C000000793 [Member]  
Shareholder Report [Line Items]  
Fund Name BNY Mellon High Yield Fund
Class Name Class I
Trading Symbol DLHRX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BNY Mellon High Yield Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at bny.com/investments/literaturecenter. You can also request this information by calling 1-800-373-9387 (inside the U.S. only) or by sending an e-mail request to info@bny.com.
Material Fund Change Notice [Text Block]
This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1-800-373-9387
Additional Information Email info@bny.com
Additional Information Website bny.com/investments/literaturecenter
Expenses [Text Block]
What were the Fund’s costs for the last six months ?
(based on a hypothetical $10,000 investment)
Share Class Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Class I* $35 0.70%**
*
During the period, fees were waived and/or expenses reimbursed pursuant to an agreement with the Fund’s investment adviser, BNY Mellon Investment Adviser, Inc.
**
Annualized.
Expenses Paid, Amount $ 35 [1]
Expense Ratio, Percent 0.70% [1],[2]
Net Assets $ 427,000,000
Holdings Count | Holding 307
Investment Company Portfolio Turnover 45.18%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (AS OF 6/30/26 )

Fund Size (Millions)
Number of Holdings
Portfolio Turnover
$427 307 45.18%
Holdings [Text Block]
Portfolio Holdings (as of 6/30/26 )
Sector Allocation (Based on Net Assets)
Graphical Representation - Top N Holdings Chart
Allocation of Holdings (Based on Net Assets)
Graphical Representation - Allocation 1 Chart
* Amount represents less than .1%.
Summary of Change Legend [Text Block]
This is a summary of certain changes to the Fund since January 1, 2026 . For more complete information, you may review the Fund’s current prospectus dated May 1, 2026 at bny.com/investments/literaturecenter or upon request at 1-800-373-9387.
Updated Prospectus Phone Number 1-800-373-9387
Updated Prospectus Web Address bny.com/investments/literaturecenter
Accountant Change Statement [Text Block] Starting January 1, 2026, Ernst & Young LLP (“EY”) became the independent registered public accounting firm of the Fund. On that date, KPMG LLP was discharged as the Fund’s accounting firm subject to completion of the December 31, 2025 fiscal year audit, which occurred on February 20, 2026. EY serves as the independent registered public accounting firm for all funds in the BNY Mellon Family of Funds.
Accountant Change Date Jan. 01, 2026
Accountant Change Disagreements [Text Block]
Changes in or Disagreements with Accountants
  • Starting January 1, 2026, Ernst & Young LLP (“EY”) became the independent registered public accounting firm of the Fund. On that date, KPMG LLP was discharged as the Fund’s accounting firm subject to completion of the December 31, 2025 fiscal year audit, which occurred on February 20, 2026. EY serves as the independent registered public accounting firm for all funds in the BNY Mellon Family of Funds. There were no disagreements with the former accounting firm during the Fund’s fiscal years ended December 31, 2025 and December 31, 2024 and the subsequent interim period through February 20, 2026.
C000000792 [Member]  
Shareholder Report [Line Items]  
Fund Name BNY Mellon High Yield Fund
Class Name Class C
Trading Symbol PTHIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BNY Mellon High Yield Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at bny.com/investments/literaturecenter. You can also request this information by calling 1-800-373-9387 (inside the U.S. only) or by sending an e-mail request to info@bny.com.
Material Fund Change Notice [Text Block]
This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1-800-373-9387
Additional Information Email info@bny.com
Additional Information Website bny.com/investments/literaturecenter
Expenses [Text Block]
What were the Fund’s costs for the last six months ?
(based on a hypothetical $10,000 investment)
Share Class Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Class C* $85 1.70%**
*
During the period, fees were waived and/or expenses reimbursed pursuant to an agreement with the Fund’s investment adviser, BNY Mellon Investment Adviser, Inc.
**
Annualized.
Expenses Paid, Amount $ 85 [3]
Expense Ratio, Percent 1.70% [3],[4]
Net Assets $ 427,000,000
Holdings Count | Holding 307
Investment Company Portfolio Turnover 45.18%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (AS OF 6/30/26 )

Fund Size (Millions)
Number of Holdings
Portfolio Turnover
$427 307 45.18%
Holdings [Text Block]
Portfolio Holdings (as of 6/30/26 )
Sector Allocation (Based on Net Assets)
Graphical Representation - Top N Holdings Chart
Allocation of Holdings (Based on Net Assets)
Graphical Representation - Allocation 1 Chart
* Amount represents less than .1%.
Summary of Change Legend [Text Block]
This is a summary of certain changes to the Fund since January 1, 2026 . For more complete information, you may review the Fund’s current prospectus dated May 1, 2026 at bny.com/investments/literaturecenter or upon request at 1-800-373-9387.
Updated Prospectus Phone Number 1-800-373-9387
Updated Prospectus Web Address bny.com/investments/literaturecenter
Accountant Change Statement [Text Block] Starting January 1, 2026, Ernst & Young LLP (“EY”) became the independent registered public accounting firm of the Fund. On that date, KPMG LLP was discharged as the Fund’s accounting firm subject to completion of the December 31, 2025 fiscal year audit, which occurred on February 20, 2026. EY serves as the independent registered public accounting firm for all funds in the BNY Mellon Family of Funds.
Accountant Change Date Jan. 01, 2026
Accountant Change Disagreements [Text Block]
Changes in or Disagreements with Accountants
  • Starting January 1, 2026, Ernst & Young LLP (“EY”) became the independent registered public accounting firm of the Fund. On that date, KPMG LLP was discharged as the Fund’s accounting firm subject to completion of the December 31, 2025 fiscal year audit, which occurred on February 20, 2026. EY serves as the independent registered public accounting firm for all funds in the BNY Mellon Family of Funds. There were no disagreements with the former accounting firm during the Fund’s fiscal years ended December 31, 2025 and December 31, 2024 and the subsequent interim period through February 20, 2026.
C000000790 [Member]  
Shareholder Report [Line Items]  
Fund Name BNY Mellon High Yield Fund
Class Name Class A
Trading Symbol DPLTX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BNY Mellon High Yield Fund (the “Fund”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at bny.com/investments/literaturecenter. You can also request this information by calling 1-800-373-9387 (inside the U.S. only) or by sending an e-mail request to info@bny.com.
Material Fund Change Notice [Text Block]
This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1-800-373-9387
Additional Information Email info@bny.com
Additional Information Website bny.com/investments/literaturecenter
Expenses [Text Block]
What were the Fund’s costs for the last six months ?
(based on a hypothetical $10,000 investment)
Share Class Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Class A* $47 0.95%**
*
During the period, fees were waived and/or expenses reimbursed pursuant to an agreement with the Fund’s investment adviser, BNY Mellon Investment Adviser, Inc.
**
Annualized.
Expenses Paid, Amount $ 47 [5]
Expense Ratio, Percent 0.95% [5],[6]
Net Assets $ 427,000,000
Holdings Count | Holding 307
Investment Company Portfolio Turnover 45.18%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (AS OF 6/30/26 )

Fund Size (Millions)
Number of Holdings
Portfolio Turnover
$427 307 45.18%
Holdings [Text Block]
Portfolio Holdings (as of 6/30/26 )
Sector Allocation (Based on Net Assets)
Graphical Representation - Top N Holdings Chart
Allocation of Holdings (Based on Net Assets)
Graphical Representation - Allocation 1 Chart
* Amount represents less than .1%.
Summary of Change Legend [Text Block]
This is a summary of certain changes to the Fund since January 1, 2026 . For more complete information, you may review the Fund’s current prospectus dated May 1, 2026 at bny.com/investments/literaturecenter or upon request at 1-800-373-9387.
Updated Prospectus Phone Number 1-800-373-9387
Updated Prospectus Web Address bny.com/investments/literaturecenter
Accountant Change Statement [Text Block] Starting January 1, 2026, Ernst & Young LLP (“EY”) became the independent registered public accounting firm of the Fund. On that date, KPMG LLP was discharged as the Fund’s accounting firm subject to completion of the December 31, 2025 fiscal year audit, which occurred on February 20, 2026. EY serves as the independent registered public accounting firm for all funds in the BNY Mellon Family of Funds.
Accountant Change Date Jan. 01, 2026
Accountant Change Disagreements [Text Block]
Changes in or Disagreements with Accountants
  • Starting January 1, 2026, Ernst & Young LLP (“EY”) became the independent registered public accounting firm of the Fund. On that date, KPMG LLP was discharged as the Fund’s accounting firm subject to completion of the December 31, 2025 fiscal year audit, which occurred on February 20, 2026. EY serves as the independent registered public accounting firm for all funds in the BNY Mellon Family of Funds. There were no disagreements with the former accounting firm during the Fund’s fiscal years ended December 31, 2025 and December 31, 2024 and the subsequent interim period through February 20, 2026.
[1] During the period, fees were waived and/or expenses reimbursed pursuant to an agreement with the Fund’s investment adviser, BNY Mellon Investment Adviser, Inc.
[2] Annualized.
[3]
During the period, fees were waived and/or expenses reimbursed pursuant to an agreement with the Fund’s investment adviser, BNY Mellon Investment Adviser, Inc.
[4]
Annualized.
[5]
During the period, fees were waived and/or expenses reimbursed pursuant to an agreement with the Fund’s investment adviser, BNY Mellon Investment Adviser, Inc.
[6]
Annualized.