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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Dec. 31, 2011
Registrant Name dei_EntityRegistrantName PIONEER FUND /MA/
Central Index Key dei_EntityCentralIndexKey 0000078713
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Apr. 27, 2012
Document Effective Date dei_DocumentEffectiveDate May 01, 2012
Prospectus Date rr_ProspectusDate May 01, 2012
Pioneer Fund
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading
PIONEER FUND
Objective [Heading] rr_ObjectiveHeading
INVESTMENT OBJECTIVES
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
Reasonable income and capital growth.
Expense [Heading] rr_ExpenseHeading
FEES AND EXPENSES OF THE FUND
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds. More information about these and other discounts is available from your investment professional and in the "Sales charges" section of the prospectus beginning on page 32 and the "Sales charges" section of the statement of additional information beginning on page 53.
Shareholder Fees: rr_ShareholderFeesAbstract  
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption
SHAREOWNER FEES
(fees paid directly from your
investment)
Operating Expenses: rr_OperatingExpensesAbstract  
Operating Expenses Caption [Text] rr_OperatingExpensesCaption
ANNUAL FUND OPERATING
EXPENSES
(expenses that you pay each year as a
percentage of the value of your
investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 1, 2013
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading
PORTFOLIO TURNOVER
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 10% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 10.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts
You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount 50,000
Expense Example: rr_ExpenseExampleAbstract  
Expense Example [Heading] rr_ExpenseExampleHeading
EXAMPLE
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods shown and then, except as indicated, redeem all of your shares at the end of those periods. It also assumes that (a) your investment has a 5% return each year and (b) the fund's total annual operating expenses remain the same except for year one (which considers the effect of the expense limitation). Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption
IF YOU REDEEM YOUR SHARES
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption
IF YOU DO NOT REDEEM YOUR SHARES
Strategy [Heading] rr_StrategyHeading
PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The fund invests in a broad group of carefully selected securities that the fund's adviser believes are reasonably priced, rather than in securities whose prices reflect a premium resulting from their current market popularity. The fund invests predominantly in equity securities. For purposes of the fund's investment policies, equity securities include common stocks, debt convertible to equity securities and other equity instruments, such as exchange-traded funds (ETFs) that invest primarily in equity securities, equity interests in real estate investment trusts (REITs), depositary receipts, warrants, rights and preferred stocks.

The fund primarily invests in securities of U.S. issuers. The fund may invest up to 15% of its total assets in equity and debt securities of non-U.S. issuers. The fund will not invest more than 5% of its total assets in the securities of emerging markets issuers.

The fund may invest up to 15% of its net assets in REITs.

The fund may also invest in investment grade and below investment grade debt securities (known as "junk bonds") and derivatives. The fund may use derivatives for a variety of purposes, including: as a hedge against adverse changes in the market price of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; and to increase the fund's return as a non-hedging strategy that may be considered speculative. The fund may also hold cash or other short-term investments.

The fund's investment adviser uses a value approach to select the fund's investments to buy and sell. The adviser seeks securities selling at reasonable prices or substantial discounts to their underlying values and then holds these securities until the market values reflect their intrinsic values. The adviser evaluates a security's potential value, including the attractiveness of its market valuation, based on the company's assets and prospects for earnings growth. In making that assessment, the adviser employs fundamental research and an evaluation of the issuer based on its financial statements and operations. In selecting securities, the adviser considers a security's potential to provide a reasonable amount of income. The adviser focuses on the quality and price of individual issuers.
Risk [Heading] rr_RiskHeading
PRINCIPAL RISKS OF INVESTING IN THE FUND
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

You could lose money on your investment in the fund. As with any mutual fund, there is no guarantee that the fund will achieve its objectives.

MARKET RISK. The values of securities held by the fund may go up or down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic, political, or regulatory conditions, inflation, changes in interest or currency rates or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. The values of securities may fall due to factors affecting a particular issuer, industry or the securities market as a whole. The stock market may perform poorly relative to other investments (this risk may be greater in the short term). The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities, including securities held by the fund. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets. The withdrawal of this support could negatively affect the value and liquidity of certain securities. In addition, legislation recently enacted in the U.S. is changing many aspects of financial regulation. The impact of the legislation on the markets, and the practical implications for market participants, may not be fully known for some time. The fund may experience a substantial or complete loss on any individual security.

VALUE STYLE RISK. The prices of securities the adviser believes are undervalued may not appreciate as expected or may go down. Value stocks may fall out of favor with investors and underperform the overall equity market.

PORTFOLIO SELECTION RISK. The adviser's judgment about a particular security or issuer, or about the economy or a particular sector, region or market segment, or about an investment strategy, may prove to be incorrect.

RISKS OF NON-U.S. INVESTMENTS. Investing in non-U.S. issuers may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced for issuers in emerging markets or to the extent that the fund invests significantly in one region or country. These risks may include different financial reporting practices and regulatory standards, less liquid trading markets, extreme price volatility, currency risks, changes in economic, political, regulatory and social conditions, sustained economic downturns, tax burdens, and investment and repatriation restrictions. Non-U.S. issuers may be located in parts of the world that have historically been prone to natural disasters.

RISKS OF INVESTMENTS IN REITS. Investing in REITs involves unique risks. They are significantly affected by the market for real estate and are dependent upon management skills and cash flow. REITs may have lower trading volumes and may be subject to more abrupt or erratic price movements than the overall securities markets. In addition to its own expenses, the fund will indirectly bear its proportionate share of any management and other expenses paid by REITs in which it invests. Many real estate companies, including REITs, utilize leverage.

DEBT SECURITIES RISK. Factors that could contribute to a decline in the market value of debt securities in the fund include rising interest rates, if the issuer or other obligor of a security held by the fund fails to pay principal and/or interest, otherwise defaults or has its credit rating downgraded or is perceived to be less creditworthy or the credit quality or value of any underlying assets declines. Junk bonds involve greater risk of loss, are subject to greater price volatility and are less liquid, especially during periods of economic uncertainty or change, than higher quality debt securities; they may also be more difficult to value. Junk bonds have a higher risk of default or are already in default and are considered speculative.

MARKET SEGMENT RISK. To the extent the fund emphasizes, from time to time, investments in a market segment, the fund will be subject to a greater degree to the risks particular to that segment, and may experience greater market fluctuation than a fund without the same focus.

DERIVATIVES RISK. Using derivatives exposes the fund to additional risks, may increase the volatility of the fund's net asset value and may not provide the result intended. Derivatives may have a leveraging effect on the fund. Changes in a derivative's value may not correlate well with the referenced asset or metric. The fund also may have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance.

LEVERAGING RISK. The value of your investment may be more volatile and other risks tend to be compounded if the fund borrows or uses derivatives or other investments, such as ETFs, that have embedded leverage. Leverage generally magnifies the effect of any increase or decrease in the value of the fund's underlying assets or creates investment risk with respect to a larger pool of assets than the fund would otherwise have. Engaging in such transactions may cause the fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations or meet segregation requirements.

EXPENSE RISK. Your actual costs of investing in the fund may be higher than the expenses shown in "Annual fund operating expenses" for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile.

Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals.

An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney
You could lose money on your investment in the fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution
An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading
THE FUND'S PAST PERFORMANCE
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year. The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Standard & Poor's 500 Index, a broad-based measure of market performance that has characteristics relevant to the fund's investment strategies. You can obtain updated performance information by visiting https://us.pioneerinvestments.com/performance or by calling 1-800-225-6292.

The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

The bar chart does not reflect any sales charge you may pay when you buy fund shares. If this amount was reflected, returns would be less than those shown.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns
The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone
1-800-225-6292
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress
https://us.pioneerinvestments.com/performance
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture
The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.
Bar Chart Table: rr_BarChartTableAbstract  
Bar Chart [Heading] rr_BarChartHeading
ANNUAL RETURN CLASS A SHARES (%)
(Year ended December 31)
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads
The bar chart does not reflect any sales charge you may pay when you buy fund shares.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

For the period covered by the bar chart:

THE HIGHEST CALENDAR QUARTERLY RETURN WAS 14.77% (04/01/2009 TO 06/30/2009).

THE LOWEST CALENDAR QUARTERLY RETURN WAS -22.10% (10/01/2008 TO 12/31/2008).
Average Annual Return: rr_AverageAnnualReturnAbstract  
Performance Table Heading rr_PerformanceTableHeading
AVERAGE ANNUAL TOTAL RETURN (%)
(for periods ended December 31, 2011)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate
After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred
The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown
After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class R, Class Y and Class Z shares shares will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor's tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.

After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class R, Class Y and Class Z shares will vary.
Pioneer Fund | Class A
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum sales charge (load) when you buy shares (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.75%
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fees rr_ManagementFeesOverAssets 0.56%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.28%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.09%
Less: Fee Waiver and Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets none [1]
Net Expenses rr_NetExpensesOverAssets 1.09% [1]
Expense Example: rr_ExpenseExampleAbstract  
1 rr_ExpenseExampleYear01 680
3 rr_ExpenseExampleYear03 902
5 rr_ExpenseExampleYear05 1,141
10 rr_ExpenseExampleYear10 1,827
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
1 rr_ExpenseExampleNoRedemptionYear01 680
3 rr_ExpenseExampleNoRedemptionYear03 902
5 rr_ExpenseExampleNoRedemptionYear05 1,141
10 rr_ExpenseExampleNoRedemptionYear10 1,827
Bar Chart Table: rr_BarChartTableAbstract  
02 rr_AnnualReturn2002 (20.26%)
03 rr_AnnualReturn2003 24.58%
04 rr_AnnualReturn2004 11.64%
05 rr_AnnualReturn2005 6.39%
06 rr_AnnualReturn2006 16.39%
07 rr_AnnualReturn2007 4.71%
08 rr_AnnualReturn2008 (34.38%)
09 rr_AnnualReturn2009 24.24%
10 rr_AnnualReturn2010 15.72%
11 rr_AnnualReturn2011 (4.59%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel
THE HIGHEST CALENDAR QUARTERLY RETURN
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 14.77%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel
THE LOWEST CALENDAR QUARTERLY RETURN
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (22.10%)
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (10.07%)
5 YEARS rr_AverageAnnualReturnYear05 (2.34%)
10 YEARS rr_AverageAnnualReturnYear10 2.01%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 11.60%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Feb. 13, 1928
Pioneer Fund | Class B
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum sales charge (load) when you buy shares (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice 4.00%
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fees rr_ManagementFeesOverAssets 0.56%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.68%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.24%
Less: Fee Waiver and Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets none [1]
Net Expenses rr_NetExpensesOverAssets 2.24% [1]
Expense Example: rr_ExpenseExampleAbstract  
1 rr_ExpenseExampleYear01 627
3 rr_ExpenseExampleYear03 1,000
5 rr_ExpenseExampleYear05 1,300
10 rr_ExpenseExampleYear10 2,284
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
1 rr_ExpenseExampleNoRedemptionYear01 227
3 rr_ExpenseExampleNoRedemptionYear03 700
5 rr_ExpenseExampleNoRedemptionYear05 1,200
10 rr_ExpenseExampleNoRedemptionYear10 2,284
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (9.44%)
5 YEARS rr_AverageAnnualReturnYear05 (2.20%)
10 YEARS rr_AverageAnnualReturnYear10 1.63%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 5.44%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Jul. 01, 1996
Pioneer Fund | Class C
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum sales charge (load) when you buy shares (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00%
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fees rr_ManagementFeesOverAssets 0.56%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.31%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.87%
Less: Fee Waiver and Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets none [1]
Net Expenses rr_NetExpensesOverAssets 1.87% [1]
Expense Example: rr_ExpenseExampleAbstract  
1 rr_ExpenseExampleYear01 290
3 rr_ExpenseExampleYear03 588
5 rr_ExpenseExampleYear05 1,011
10 rr_ExpenseExampleYear10 2,190
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
1 rr_ExpenseExampleNoRedemptionYear01 190
3 rr_ExpenseExampleNoRedemptionYear03 588
5 rr_ExpenseExampleNoRedemptionYear05 1,011
10 rr_ExpenseExampleNoRedemptionYear10 2,190
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (5.33%) [2]
5 YEARS rr_AverageAnnualReturnYear05 (1.96%) [2]
10 YEARS rr_AverageAnnualReturnYear10 1.81% [2]
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 5.49% [2]
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Jul. 01, 1996 [2]
Pioneer Fund | Class R
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum sales charge (load) when you buy shares (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fees rr_ManagementFeesOverAssets 0.56%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.32%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.38%
Less: Fee Waiver and Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets none [1]
Net Expenses rr_NetExpensesOverAssets 1.38% [1]
Expense Example: rr_ExpenseExampleAbstract  
1 rr_ExpenseExampleYear01 140
3 rr_ExpenseExampleYear03 437
5 rr_ExpenseExampleYear05 755
10 rr_ExpenseExampleYear10 1,657
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
1 rr_ExpenseExampleNoRedemptionYear01 140
3 rr_ExpenseExampleNoRedemptionYear03 437
5 rr_ExpenseExampleNoRedemptionYear05 755
10 rr_ExpenseExampleNoRedemptionYear10 1,657
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (4.85%)
5 YEARS rr_AverageAnnualReturnYear05 (1.40%)
10 YEARS rr_AverageAnnualReturnYear10   
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 6.13%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Apr. 01, 2003
Pioneer Fund | Class Y
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum sales charge (load) when you buy shares (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fees rr_ManagementFeesOverAssets 0.56%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.16%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.72%
Less: Fee Waiver and Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets none [1]
Net Expenses rr_NetExpensesOverAssets 0.72% [1]
Expense Example: rr_ExpenseExampleAbstract  
1 rr_ExpenseExampleYear01 74
3 rr_ExpenseExampleYear03 230
5 rr_ExpenseExampleYear05 401
10 rr_ExpenseExampleYear10 894
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
1 rr_ExpenseExampleNoRedemptionYear01 74
3 rr_ExpenseExampleNoRedemptionYear03 230
5 rr_ExpenseExampleNoRedemptionYear05 401
10 rr_ExpenseExampleNoRedemptionYear10 894
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (4.22%)
5 YEARS rr_AverageAnnualReturnYear05 (0.76%)
10 YEARS rr_AverageAnnualReturnYear10 3.05%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 2.15%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate May 06, 1999
Pioneer Fund | Class Z
  
Shareholder Fees: rr_ShareholderFeesAbstract  
Maximum sales charge (load) when you buy shares (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses: rr_OperatingExpensesAbstract  
Management Fees rr_ManagementFeesOverAssets 0.56%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.43%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.99%
Less: Fee Waiver and Expense Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.14%) [1]
Net Expenses rr_NetExpensesOverAssets 0.85% [1]
Expense Example: rr_ExpenseExampleAbstract  
1 rr_ExpenseExampleYear01 87
3 rr_ExpenseExampleYear03 301
5 rr_ExpenseExampleYear05 533
10 rr_ExpenseExampleYear10 1,200
Expense Example, No Redemption: rr_ExpenseExampleNoRedemptionAbstract  
1 rr_ExpenseExampleNoRedemptionYear01 87
3 rr_ExpenseExampleNoRedemptionYear03 301
5 rr_ExpenseExampleNoRedemptionYear05 533
10 rr_ExpenseExampleNoRedemptionYear10 1,200
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (4.34%)
5 YEARS rr_AverageAnnualReturnYear05   
10 YEARS rr_AverageAnnualReturnYear10   
SINCE INCEPTION rr_AverageAnnualReturnSinceInception (2.01%)
INCEPTION DATE rr_AverageAnnualReturnInceptionDate May 01, 2007
Pioneer Fund | Return after taxes on distributions | Class A
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (10.23%)
5 YEARS rr_AverageAnnualReturnYear05 (2.83%)
10 YEARS rr_AverageAnnualReturnYear10 1.57%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 8.22%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Feb. 13, 1928
Pioneer Fund | Return after taxes on distributions and sale of shares | Class A
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (6.33%)
5 YEARS rr_AverageAnnualReturnYear05 (2.02%)
10 YEARS rr_AverageAnnualReturnYear10 1.67%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 8.15%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Feb. 13, 1928
Pioneer Fund | Standard & Poor's 500 Index (reflects no deduction for fees, expenses or taxes)
  
Average Annual Return: rr_AverageAnnualReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 2.11%
5 YEARS rr_AverageAnnualReturnYear05 (0.25%)
10 YEARS rr_AverageAnnualReturnYear10 2.92%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception    [3]
[1] The fund's investment adviser has contractually agreed to limit ordinary operating expenses (ordinary operating expenses means all fund expenses other than extraordinary expenses, such as litigation, taxes and brokerage commissions) to the extent required to reduce Class Z shares expenses to 0.85% of the average daily net assets attributable to Class Z shares. This expense limitation is in effect through May 1, 2013. There can be no assurance that the adviser will extend the expense limitation beyond such time. While in effect, the arrangement may be terminated for a class only by agreement of the adviser and the Board of Trustees.
[2] The performance of Class C shares does not reflect the 1% front-end sales charge in effect prior to February 1, 2004. If you paid a 1% sales charge, your returns would be lower than those shown above.
[3] Index return information is not available since the fund's inception.