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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Oct. 31, 2014
Registrant Name dei_EntityRegistrantName PRINCIPAL FUNDS INC
Central Index Key dei_EntityCentralIndexKey 0000898745
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate May 18, 2015
Document Effective Date dei_DocumentEffectiveDate May 18, 2015
Prospectus Date rr_ProspectusDate May 18, 2015
Tax-Exempt Bond Fund [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading TAX-EXEMPT BOND FUND
Objective [Heading] rr_ObjectiveHeading Objective:
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The Fund seeks to provide a high level of income that is exempt from federal income tax while protecting investors’ capital.
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.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment):
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)
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 22.3% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 22.30%rr_PortfolioTurnoverRate
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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.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption The Example assumes that you invest $10,000 in the Fund for the time periods indicated. The Example assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Under normal circumstances, the Fund invests at least 80% of its net assets, plus any borrowings for investment purposes, in tax-exempt bonds (securities issued by or on behalf of state or local governments and other public authorities) at the time of each purchase. Many of these are from California and Illinois. Generally, municipal obligations pay interest that is exempt from federal income tax. The Fund also invests in inverse floating rate obligations, which are generally more volatile than other types of municipal obligations and may involve leverage. The Fund may invest up to 20% of its assets in below investment grade bonds (sometimes called “high yield bonds” or "junk bonds") which are rated at the time of purchase Ba1 or lower by Moody's and BB+ or lower by S&P (if the bond has been rated by only one of those agencies, that rating will determine whether the bond is below investment grade; if the bond has not been rated by either of those agencies, the Sub-Advisor will determine whether the bond is of a quality comparable to those rated below investment grade). Under normal circumstances, the Fund maintains an average portfolio duration that is within ±50% of the duration of the Barclays Municipal Bond Index, which as of December 31, 2014 was 4.69 years.
During the fiscal year ended October 31, 2014, the average ratings of the Fund’s fixed-income assets, based on market value at each month-end, were as follows (all ratings are by Moody’s):
11.87% in securities rated Aaa
9.20% in securities rated Baa
0.08% in securities rated Caa
0.00% in securities rated D
45.10% in securities rated Aa
4.38% in securities rated Ba
0.00% in securities rated Ca
7.46% in securities not rated
19.42% in securities rated A
2.49% in securities rated B
0.00% in securities rated C
 
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
The value of your investment in the Fund changes with the value of the Fund's investments. Many factors affect that value, and it is possible to lose money by investing in the Fund. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The principal risks of investing in the Fund, in alphabetical order, are:
Counterparty Risk. Counterparty risk is the risk that the counterparty to a derivatives contract or repurchase agreement, the borrower of a portfolio’s securities, or other obligation, will be unable or unwilling to make timely principal, interest, or settlement payments, or otherwise to honor its obligations.
Fixed-Income Securities Risk. Fixed-income securities are subject to interest rate risk and credit quality risk. The market value of fixed-income securities generally declines when interest rates rise, and an issuer of fixed-income securities could default on its payment obligations.
Geographic Concentration Risk. A fund that invests significant portions of its assets in particular geographic areas (a particular state, such as California or Illinois, or a particular country or region) has greater exposure than other funds to economic conditions and developments in those areas.
High Yield Securities Risk. High yield fixed-income securities (commonly referred to as "junk bonds") are subject to greater credit quality risk than higher rated fixed-income securities and should be considered speculative.
Inverse Floating Rate Investments. Inverse floating rate investments are extremely sensitive to changes in interest rates and in some cases their market value may be extremely volatile.
Leverage Risk. Leverage created by borrowing or certain types of transactions or investments may impair the fund's liquidity, cause it to liquidate positions at an unfavorable time, increase volatility of the fund's net asset value, or diminish the fund's performance.
Municipal Securities Risk. Principal and interest payments on municipal securities may not be guaranteed by the issuing body and may be payable only from a particular source. That source may not perform as expected and payment obligations may not be made or made on time.
Portfolio Duration Risk. Portfolio duration is a measure of the expected life of a fixed-income security and its sensitivity to changes in interest rates. The longer a fund's average portfolio duration, the more sensitive the fund will be to changes in interest rates.
Risk Lose Money [Text] rr_RiskLoseMoney Many factors affect that value, and it is possible to lose money by investing in the Fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution An investment in the Fund is not a deposit of a bank 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 Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The following information provides some indication of the risks of investing in the Fund. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. You may get updated performance information by calling 1-800-222-5852 or online at www.principal.com.
The bar chart shows the investment returns of the Fund’s Institutional Class shares for each full calendar year of operations for 10 years (or, if shorter, the life of the Fund). The table shows, for Institutional Class shares of the Fund and for the last one, five, and ten calendar year periods (or, if shorter, the life of the Fund), how the Fund's average annual total returns compare with those of one or more broad measures of market performance.
For periods prior the inception date of the Institutional Class shares (May 18, 2015), performance of the Institutional Class shares is based on the performance of the Fund's Class A shares adjusted to reflect the fees and expenses of Institutional Class shares; these adjustments result in performance for such periods that is no higher than the historical performance of the Class A shares.
The Fund commenced operations after succeeding to the operations of another fund on January 12, 2007. Performance for periods prior to that date is based on the performance of the predecessor fund, which commenced operations on January 3, 1977.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in the Fund. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. You may get updated performance information by calling 1-800-222-5852 or online at www.principal.com.The bar chart shows the investment returns of the Fund’s Institutional Class shares for each full calendar year of operations for 10 years (or, if shorter, the life of the Fund). The table shows, for Institutional Class shares of the Fund and for the last one, five, and ten calendar year periods (or, if shorter, the life of the Fund), how the Fund's average annual total returns compare with those of one or more broad measures of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-222-5852
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.principal.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Total Returns as of December 31 (Institutional Class shares)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Highest return for a quarter during the period of the bar chart above:
Q3 '09
10.13
 %
Lowest return for a quarter during the period of the bar chart above:
Q4 '08
(5.96
)%
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 Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
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 an investor’s tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns For the periods ended December 31, 2014
Tax-Exempt Bond Fund [Member] | Barclays Municipal Bond Index [Member]  
Risk/Return: rr_RiskReturnAbstract  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses, or taxes)
Label rr_AverageAnnualReturnLabel Barclays Municipal Bond Index (reflects no deduction for fees, expenses, or taxes)
1 Year rr_AverageAnnualReturnYear01 9.05%rr_AverageAnnualReturnYear01
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5 Years rr_AverageAnnualReturnYear05 5.16%rr_AverageAnnualReturnYear05
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10 Years rr_AverageAnnualReturnYear10 4.74%rr_AverageAnnualReturnYear10
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Tax-Exempt Bond Fund [Member] | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol PITEX
Shareholder Fee, Other rr_ShareholderFeeOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.45%rr_ManagementFeesOverAssets
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Component1 Other Expenses rr_Component1OtherExpensesOverAssets 0.03%rr_Component1OtherExpensesOverAssets
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Component2 Other Expenses rr_Component2OtherExpensesOverAssets 0.13%rr_Component2OtherExpensesOverAssets
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Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.61%rr_ExpensesOverAssets
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Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets none [2]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.61%rr_NetExpensesOverAssets
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Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2017
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 62rr_ExpenseExampleYear01
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Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 195rr_ExpenseExampleYear03
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Annual Return 2005 rr_AnnualReturn2005 3.14%rr_AnnualReturn2005
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Annual Return 2006 rr_AnnualReturn2006 5.22%rr_AnnualReturn2006
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Annual Return 2007 rr_AnnualReturn2007 0.17%rr_AnnualReturn2007
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Annual Return 2008 rr_AnnualReturn2008 (12.15%)rr_AnnualReturn2008
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Annual Return 2009 rr_AnnualReturn2009 20.36%rr_AnnualReturn2009
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Annual Return 2010 rr_AnnualReturn2010 1.80%rr_AnnualReturn2010
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Annual Return 2011 rr_AnnualReturn2011 11.03%rr_AnnualReturn2011
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Annual Return 2012 rr_AnnualReturn2012 9.02%rr_AnnualReturn2012
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Annual Return 2013 rr_AnnualReturn2013 (4.67%)rr_AnnualReturn2013
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Annual Return 2014 rr_AnnualReturn2014 12.01%rr_AnnualReturn2014
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Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest return for a quarter during the period of the bar chart above:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 10.13%rr_BarChartHighestQuarterlyReturn
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Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest return for a quarter during the period of the bar chart above:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (5.96%)rr_BarChartLowestQuarterlyReturn
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Label rr_AverageAnnualReturnLabel Institutional Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 12.01%rr_AverageAnnualReturnYear01
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5 Years rr_AverageAnnualReturnYear05 5.64%rr_AverageAnnualReturnYear05
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10 Years rr_AverageAnnualReturnYear10 4.22%rr_AverageAnnualReturnYear10
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Tax-Exempt Bond Fund [Member] | Institutional Class | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Institutional Class Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 12.01%rr_AverageAnnualReturnYear01
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5 Years rr_AverageAnnualReturnYear05 5.64%rr_AverageAnnualReturnYear05
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10 Years rr_AverageAnnualReturnYear10 4.19%rr_AverageAnnualReturnYear10
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Tax-Exempt Bond Fund [Member] | Institutional Class | After Taxes on Distributions and Sales  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Institutional Class Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 8.84%rr_AverageAnnualReturnYear01
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5 Years rr_AverageAnnualReturnYear05 5.39%rr_AverageAnnualReturnYear05
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10 Years rr_AverageAnnualReturnYear10 4.25%rr_AverageAnnualReturnYear10
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[1] Based on estimated amounts for the current fiscal year.
[2] Principal Management Corporation ("Principal"), the investment advisor, has contractually agreed to limit the Fund’s expenses by paying, if necessary, expenses normally payable by the Fund, (excluding interest expense, expenses related to fund investments, acquired fund fees and expenses, and other extraordinary expenses) to maintain a total level of operating expenses (expressed as a percent of average net assets on an annualized basis) not to exceed 0.60% for Institutional Class shares. It is expected that the expense limit will continue through the period ending February 28, 2017; however, Principal Funds, Inc. and Principal, the parties to the agreement, may mutually agree to terminate the expense limit prior to the end of the period.