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Shareholder Report
 6 Months Ended
Jun. 30, 2024
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name PIONEER FUND /MA/
Entity Central Index Key 0000078713
Document Period End Date Jun. 30, 2024
C000011118 [Member]  
Shareholder Report [Line Items]  
Fund Name Pioneer Fund
Class Name Class A
Trading Symbol PIODX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Pioneer Fund (“Fund”) for the period of January 1, 2024 to June 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at https://www.amundi.com/usinvestors/Resources/Shareholder-Reports. You can also request this information by contacting us at 1-800-225-6292.
Material Fund Change Notice [Text Block] This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1-800-225-6292
Additional Information Website https://www.amundi.com/usinvestors/Resources/Shareholder-Reports
Expenses [Text Block]
What were the Fund costs for the last six months?
(Based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Class A $50 0.91%^
​^
Annualized
Expenses Paid, Amount $ 50
Expense Ratio, Percent 0.91% [1]
Net Assets $ 8,928,920,767
Holdings Count | Holding 45 [2]
Investment Company Portfolio Turnover 28.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS
(as of June 30, 2024)
Fund net assets $8,928,920,767%
Total number of portfolio holdings $45%^^
Portfolio turnover rate $28%
^^
Short-term investments and derivative contracts other than purchased options are not included.
Holdings [Text Block]
SECTOR DISTRIBUTION
(as of June 30, 2024)*
Information Technology 34.1%
Financials 16.4%
Health Care 10.6%
Materials 8.6%
Consumer Discretionary 8.1%
Industrials 7.9%
Communication Services 6.3%
Consumer Staples 4.2%
Energy 3.8%
​*
As a percentage of total investments excluding short-term investments and all derivative contracts except for options purchased.
Material Fund Change [Text Block]
Material Fund Changes
Amundi Asset Management US, Inc. (the “Adviser”), the Fund’s investment adviser, is currently an indirect, wholly-owned subsidiary of Amundi.  On July 9, 2024, Amundi announced that it had entered into a definitive agreement with Victory Capital Holdings, Inc. (“Victory Capital”) to combine the Adviser with Victory Capital, and for Amundi to become a strategic shareholder of Victory Capital (the “Transaction”).  Victory Capital is headquartered in San Antonio, Texas.  The closing of the Transaction is subject to certain regulatory approvals and other conditions.  There is no assurance that the Transaction will close.
The closing of the Transaction would cause the Fund’s current investment advisory agreement with the Adviser to terminate.  Under the terms of the Transaction, the Fund’s Board of Trustees will be asked to approve a reorganization of the Fund into a corresponding, newly established Victory Fund advised by Victory Capital Management Inc., an affiliate of Victory Capital.  The proposed reorganization of the Fund would be sought in connection with the closing of the Transaction.  If approved by the Board, the proposal to reorganize the Fund will be submitted to the shareholders of the Fund for their approval.  There is no assurance that the Board or the shareholders of the Fund will approve the proposal to reorganize the Fund.
This is a summary of certain planned changes to the Fund.  For more complete information, you may review the Fund's next prospectus, which we expect to be available by May 1, 2025 at https://www.amundi.com/usinvestors/Products/Mutual-Funds or upon request at 1-800-225-6292.
Updated Prospectus Phone Number 1-800-225-6292
Updated Prospectus Web Address https://www.amundi.com/usinvestors/Products/Mutual-Funds
Accountant Change Disagreements [Text Block]
Changes in and Disagreements with Accountants
On March 25, 2024, Ernst & Young LLP (the “Prior Auditor”) resigned as the independent registered public accounting firm of the Fund. There were no disagreements with the Prior Auditor during the two most recent fiscal years and the subsequent interim period through March 25, 2024.
On March 25, 2024, the Audit Committee of the Board approved, and on March 25, 2024, the Board approved, Deloitte & Touche LLP as the independent registered accounting firm of the Fund for fiscal periods ending after March 25, 2024.
C000011120 [Member]  
Shareholder Report [Line Items]  
Fund Name Pioneer Fund
Class Name Class C
Trading Symbol PCODX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Pioneer Fund (“Fund”) for the period of January 1, 2024 to June 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at https://www.amundi.com/usinvestors/Resources/Shareholder-Reports. You can also request this information by contacting us at 1-800-225-6292.
Material Fund Change Notice [Text Block] This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1-800-225-6292
Additional Information Website https://www.amundi.com/usinvestors/Resources/Shareholder-Reports
Expenses [Text Block]
What were the Fund costs for the last six months?
(Based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Class C $92 1.70%^
​^
Annualized
Expenses Paid, Amount $ 92
Expense Ratio, Percent 1.70% [3]
Net Assets $ 8,928,920,767
Holdings Count | Holding 45 [4]
Investment Company Portfolio Turnover 28.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS
(as of June 30, 2024)
Fund net assets $8,928,920,767%
Total number of portfolio holdings $45%^^
Portfolio turnover rate $28%
^^
Short-term investments and derivative contracts other than purchased options are not included.
Holdings [Text Block]
SECTOR DISTRIBUTION
(as of June 30, 2024)*
Information Technology 34.1%
Financials 16.4%
Health Care 10.6%
Materials 8.6%
Consumer Discretionary 8.1%
Industrials 7.9%
Communication Services 6.3%
Consumer Staples 4.2%
Energy 3.8%
​*
As a percentage of total investments excluding short-term investments and all derivative contracts except for options purchased.
Material Fund Change [Text Block]
Material Fund Changes
Amundi Asset Management US, Inc. (the “Adviser”), the Fund’s investment adviser, is currently an indirect, wholly-owned subsidiary of Amundi.  On July 9, 2024, Amundi announced that it had entered into a definitive agreement with Victory Capital Holdings, Inc. (“Victory Capital”) to combine the Adviser with Victory Capital, and for Amundi to become a strategic shareholder of Victory Capital (the “Transaction”).  Victory Capital is headquartered in San Antonio, Texas.  The closing of the Transaction is subject to certain regulatory approvals and other conditions.  There is no assurance that the Transaction will close.
The closing of the Transaction would cause the Fund’s current investment advisory agreement with the Adviser to terminate.  Under the terms of the Transaction, the Fund’s Board of Trustees will be asked to approve a reorganization of the Fund into a corresponding, newly established Victory Fund advised by Victory Capital Management Inc., an affiliate of Victory Capital.  The proposed reorganization of the Fund would be sought in connection with the closing of the Transaction.  If approved by the Board, the proposal to reorganize the Fund will be submitted to the shareholders of the Fund for their approval.  There is no assurance that the Board or the shareholders of the Fund will approve the proposal to reorganize the Fund.
This is a summary of certain planned changes to the Fund.  For more complete information, you may review the Fund's next prospectus, which we expect to be available by May 1, 2025 at https://www.amundi.com/usinvestors/Products/Mutual-Funds or upon request at 1-800-225-6292.
Updated Prospectus Phone Number 1-800-225-6292
Updated Prospectus Web Address https://www.amundi.com/usinvestors/Products/Mutual-Funds
Accountant Change Disagreements [Text Block]
Changes in and Disagreements with Accountants
On March 25, 2024, Ernst & Young LLP (the “Prior Auditor”) resigned as the independent registered public accounting firm of the Fund. There were no disagreements with the Prior Auditor during the two most recent fiscal years and the subsequent interim period through March 25, 2024.
On March 25, 2024, the Audit Committee of the Board approved, and on March 25, 2024, the Board approved, Deloitte & Touche LLP as the independent registered accounting firm of the Fund for fiscal periods ending after March 25, 2024.
C000202421 [Member]  
Shareholder Report [Line Items]  
Fund Name Pioneer Fund
Class Name Class K
Trading Symbol PIOKX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Pioneer Fund (“Fund”) for the period of January 1, 2024 to June 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at https://www.amundi.com/usinvestors/Resources/Shareholder-Reports. You can also request this information by contacting us at 1-800-225-6292.
Material Fund Change Notice [Text Block] This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1-800-225-6292
Additional Information Website https://www.amundi.com/usinvestors/Resources/Shareholder-Reports
Expenses [Text Block]
What were the Fund costs for the last six months?
(Based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Class K $34 0.62%^
​^
Annualized
Expenses Paid, Amount $ 34
Expense Ratio, Percent 0.62% [5]
Net Assets $ 8,928,920,767
Holdings Count | Holding 45 [6]
Investment Company Portfolio Turnover 28.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS
(as of June 30, 2024)
Fund net assets $8,928,920,767%
Total number of portfolio holdings $45%^^
Portfolio turnover rate $28%
^^
Short-term investments and derivative contracts other than purchased options are not included.
Holdings [Text Block]
SECTOR DISTRIBUTION
(as of June 30, 2024)*
Information Technology 34.1%
Financials 16.4%
Health Care 10.6%
Materials 8.6%
Consumer Discretionary 8.1%
Industrials 7.9%
Communication Services 6.3%
Consumer Staples 4.2%
Energy 3.8%
​*
As a percentage of total investments excluding short-term investments and all derivative contracts except for options purchased.
Material Fund Change [Text Block]
Material Fund Changes
Amundi Asset Management US, Inc. (the “Adviser”), the Fund’s investment adviser, is currently an indirect, wholly-owned subsidiary of Amundi.  On July 9, 2024, Amundi announced that it had entered into a definitive agreement with Victory Capital Holdings, Inc. (“Victory Capital”) to combine the Adviser with Victory Capital, and for Amundi to become a strategic shareholder of Victory Capital (the “Transaction”).  Victory Capital is headquartered in San Antonio, Texas.  The closing of the Transaction is subject to certain regulatory approvals and other conditions.  There is no assurance that the Transaction will close.
The closing of the Transaction would cause the Fund’s current investment advisory agreement with the Adviser to terminate.  Under the terms of the Transaction, the Fund’s Board of Trustees will be asked to approve a reorganization of the Fund into a corresponding, newly established Victory Fund advised by Victory Capital Management Inc., an affiliate of Victory Capital.  The proposed reorganization of the Fund would be sought in connection with the closing of the Transaction.  If approved by the Board, the proposal to reorganize the Fund will be submitted to the shareholders of the Fund for their approval.  There is no assurance that the Board or the shareholders of the Fund will approve the proposal to reorganize the Fund.
This is a summary of certain planned changes to the Fund.  For more complete information, you may review the Fund's next prospectus, which we expect to be available by May 1, 2025 at https://www.amundi.com/usinvestors/Products/Mutual-Funds or upon request at 1-800-225-6292.
Updated Prospectus Phone Number 1-800-225-6292
Updated Prospectus Web Address https://www.amundi.com/usinvestors/Products/Mutual-Funds
Accountant Change Disagreements [Text Block]
Changes in and Disagreements with Accountants
On March 25, 2024, Ernst & Young LLP (the “Prior Auditor”) resigned as the independent registered public accounting firm of the Fund. There were no disagreements with the Prior Auditor during the two most recent fiscal years and the subsequent interim period through March 25, 2024.
On March 25, 2024, the Audit Committee of the Board approved, and on March 25, 2024, the Board approved, Deloitte & Touche LLP as the independent registered accounting firm of the Fund for fiscal periods ending after March 25, 2024.
C000011122 [Member]  
Shareholder Report [Line Items]  
Fund Name Pioneer Fund
Class Name Class R
Trading Symbol PIORX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Pioneer Fund (“Fund”) for the period of January 1, 2024 to June 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at https://www.amundi.com/usinvestors/Resources/Shareholder-Reports. You can also request this information by contacting us at 1-800-225-6292.
Material Fund Change Notice [Text Block] This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1-800-225-6292
Additional Information Website https://www.amundi.com/usinvestors/Resources/Shareholder-Reports
Expenses [Text Block]
What were the Fund costs for the last six months?
(Based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Class R $72 1.32%^
​^
Annualized
Expenses Paid, Amount $ 72
Expense Ratio, Percent 1.32% [7]
Net Assets $ 8,928,920,767
Holdings Count | Holding 45 [8]
Investment Company Portfolio Turnover 28.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS
(as of June 30, 2024)
Fund net assets $8,928,920,767%
Total number of portfolio holdings $45%^^
Portfolio turnover rate $28%
^^
Short-term investments and derivative contracts other than purchased options are not included.
Holdings [Text Block]
SECTOR DISTRIBUTION
(as of June 30, 2024)*
Information Technology 34.1%
Financials 16.4%
Health Care 10.6%
Materials 8.6%
Consumer Discretionary 8.1%
Industrials 7.9%
Communication Services 6.3%
Consumer Staples 4.2%
Energy 3.8%
​*
As a percentage of total investments excluding short-term investments and all derivative contracts except for options purchased.
Material Fund Change [Text Block]
Material Fund Changes
Amundi Asset Management US, Inc. (the “Adviser”), the Fund’s investment adviser, is currently an indirect, wholly-owned subsidiary of Amundi.  On July 9, 2024, Amundi announced that it had entered into a definitive agreement with Victory Capital Holdings, Inc. (“Victory Capital”) to combine the Adviser with Victory Capital, and for Amundi to become a strategic shareholder of Victory Capital (the “Transaction”).  Victory Capital is headquartered in San Antonio, Texas.  The closing of the Transaction is subject to certain regulatory approvals and other conditions.  There is no assurance that the Transaction will close.
The closing of the Transaction would cause the Fund’s current investment advisory agreement with the Adviser to terminate.  Under the terms of the Transaction, the Fund’s Board of Trustees will be asked to approve a reorganization of the Fund into a corresponding, newly established Victory Fund advised by Victory Capital Management Inc., an affiliate of Victory Capital.  The proposed reorganization of the Fund would be sought in connection with the closing of the Transaction.  If approved by the Board, the proposal to reorganize the Fund will be submitted to the shareholders of the Fund for their approval.  There is no assurance that the Board or the shareholders of the Fund will approve the proposal to reorganize the Fund.
This is a summary of certain planned changes to the Fund.  For more complete information, you may review the Fund's next prospectus, which we expect to be available by May 1, 2025 at https://www.amundi.com/usinvestors/Products/Mutual-Funds or upon request at 1-800-225-6292.
Updated Prospectus Phone Number 1-800-225-6292
Updated Prospectus Web Address https://www.amundi.com/usinvestors/Products/Mutual-Funds
Accountant Change Disagreements [Text Block]
Changes in and Disagreements with Accountants
On March 25, 2024, Ernst & Young LLP (the “Prior Auditor”) resigned as the independent registered public accounting firm of the Fund. There were no disagreements with the Prior Auditor during the two most recent fiscal years and the subsequent interim period through March 25, 2024.
On March 25, 2024, the Audit Committee of the Board approved, and on March 25, 2024, the Board approved, Deloitte & Touche LLP as the independent registered accounting firm of the Fund for fiscal periods ending after March 25, 2024.
C000011121 [Member]  
Shareholder Report [Line Items]  
Fund Name Pioneer Fund
Class Name Class Y
Trading Symbol PYODX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Pioneer Fund (“Fund”) for the period of January 1, 2024 to June 30, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at https://www.amundi.com/usinvestors/Resources/Shareholder-Reports. You can also request this information by contacting us at 1-800-225-6292.
Material Fund Change Notice [Text Block] This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1-800-225-6292
Additional Information Website https://www.amundi.com/usinvestors/Resources/Shareholder-Reports
Expenses [Text Block]
What were the Fund costs for the last six months?
(Based on a hypothetical $10,000 investment)
Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment
Class Y $34 0.62%^
​^
Annualized
Expenses Paid, Amount $ 34
Expense Ratio, Percent 0.62% [9]
Net Assets $ 8,928,920,767
Holdings Count | Holding 45 [10]
Investment Company Portfolio Turnover 28.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS
(as of June 30, 2024)
Fund net assets $8,928,920,767%
Total number of portfolio holdings $45%^^
Portfolio turnover rate $28%
^^
Short-term investments and derivative contracts other than purchased options are not included.
Holdings [Text Block]
SECTOR DISTRIBUTION
(as of June 30, 2024)*
Information Technology 34.1%
Financials 16.4%
Health Care 10.6%
Materials 8.6%
Consumer Discretionary 8.1%
Industrials 7.9%
Communication Services 6.3%
Consumer Staples 4.2%
Energy 3.8%
​*
As a percentage of total investments excluding short-term investments and all derivative contracts except for options purchased.
Material Fund Change [Text Block]
Material Fund Changes
Amundi Asset Management US, Inc. (the “Adviser”), the Fund’s investment adviser, is currently an indirect, wholly-owned subsidiary of Amundi.  On July 9, 2024, Amundi announced that it had entered into a definitive agreement with Victory Capital Holdings, Inc. (“Victory Capital”) to combine the Adviser with Victory Capital, and for Amundi to become a strategic shareholder of Victory Capital (the “Transaction”).  Victory Capital is headquartered in San Antonio, Texas.  The closing of the Transaction is subject to certain regulatory approvals and other conditions.  There is no assurance that the Transaction will close.
The closing of the Transaction would cause the Fund’s current investment advisory agreement with the Adviser to terminate.  Under the terms of the Transaction, the Fund’s Board of Trustees will be asked to approve a reorganization of the Fund into a corresponding, newly established Victory Fund advised by Victory Capital Management Inc., an affiliate of Victory Capital.  The proposed reorganization of the Fund would be sought in connection with the closing of the Transaction.  If approved by the Board, the proposal to reorganize the Fund will be submitted to the shareholders of the Fund for their approval.  There is no assurance that the Board or the shareholders of the Fund will approve the proposal to reorganize the Fund.
This is a summary of certain planned changes to the Fund.  For more complete information, you may review the Fund's next prospectus, which we expect to be available by May 1, 2025 at https://www.amundi.com/usinvestors/Products/Mutual-Funds or upon request at 1-800-225-6292.
Updated Prospectus Phone Number 1-800-225-6292
Updated Prospectus Web Address https://www.amundi.com/usinvestors/Products/Mutual-Funds
Accountant Change Disagreements [Text Block]
Changes in and Disagreements with Accountants
On March 25, 2024, Ernst & Young LLP (the “Prior Auditor”) resigned as the independent registered public accounting firm of the Fund. There were no disagreements with the Prior Auditor during the two most recent fiscal years and the subsequent interim period through March 25, 2024.
On March 25, 2024, the Audit Committee of the Board approved, and on March 25, 2024, the Board approved, Deloitte & Touche LLP as the independent registered accounting firm of the Fund for fiscal periods ending after March 25, 2024.
[1] Annualized
[2] Short-term investments and derivative contracts other than purchased options are not included.
[3] Annualized
[4] Short-term investments and derivative contracts other than purchased options are not included.
[5] Annualized
[6] Short-term investments and derivative contracts other than purchased options are not included.
[7] Annualized
[8] Short-term investments and derivative contracts other than purchased options are not included.
[9] Annualized
[10] Short-term investments and derivative contracts other than purchased options are not included.