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Label Element Value
Prospectus: rr_ProspectusTable  
Document Type dei_DocumentType 497
Document Period End Date dei_DocumentPeriodEndDate Aug. 31, 2016
Entity Registrant Name dei_EntityRegistrantName PRINCIPAL FUNDS INC
Central Index Key dei_EntityCentralIndexKey 0000898745
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Jan. 13, 2017
Document Effective Date dei_DocumentEffectiveDate Jan. 13, 2017
Prospectus Date rr_ProspectusDate Dec. 31, 2016
Supplement [Text Block] ck0000898745_SupplementTextBlock
Principal Funds, Inc.

Supplement dated January 13, 2017
to the Statutory Prospectus dated December 31, 2016
This supplement updates information currently in the Statutory Prospectus. Please retain this supplement for future reference.
Capital Securities Fund [Member]  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading CAPITAL SECURITIES FUND
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading In the Performance section, delete the Average Annual Total Returns table and the subsequent paragraph, and replace with the following:
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 One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown for Class S shares only and would be different for the other share classes.
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. After-tax returns are shown for Class S shares only and would be different for the other share classes.
Effective January 1, 2017, the Fund’s primary benchmark changed from the BofA Merrill Lynch U.S. Capital Securities Index to the BofA Merrill Lynch U.S. All Capital Securities Index because the BofA Merrill Lynch U.S. All Capital Securities Index more closely aligns with the Fund’s investments.
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns For the periods ended 12/31/2015
Capital Securities Fund [Member] | BofA Merrill Lynch U.S. All Capital Securities Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses, or taxes)
1 Year rr_AverageAnnualReturnYear01 5.43%
Since Inception rr_AverageAnnualReturnSinceInception 7.13%
Capital Securities Fund [Member] | BofA Merrill Lynch U.S. Capital Securities Index [Member]  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses, or taxes)
1 Year rr_AverageAnnualReturnYear01 0.86%
Since Inception rr_AverageAnnualReturnSinceInception 3.54%
Capital Securities Fund [Member] | Class S  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 3.70%
Since Inception rr_AverageAnnualReturnSinceInception 4.14%
Capital Securities Fund [Member] | Class S | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 1.44%
Since Inception rr_AverageAnnualReturnSinceInception 1.90%
Capital Securities Fund [Member] | Class S | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 2.34%
Since Inception rr_AverageAnnualReturnSinceInception 2.24%
Preferred Securities Fund [Member]  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading PREFERRED SECURITIES FUND
Strategy [Heading] rr_StrategyHeading Delete the second paragraph under Principal Investment Strategies, and replace with the following:
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Most of the securities purchased by the Fund are preferred securities of companies rated at the time of purchase BBB- or higher by S&P Global Ratings ("S&P Global") or Baa3 or higher by Moody's Investors Service, Inc. ("Moody's") or, if unrated, of comparable quality in the opinion of the Sub-Advisor. The Fund also invests up to 40% of its assets in below investment grade preferred securities and 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 Global (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).
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading In the Performance section, delete the Average Annual Total Returns table and the subsequent paragraphs, and replace with the following:
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex Performance of a blended index shows how the Fund's performance compares to a blend of indices with similar investment objectives. Performance of the components of the blended index are also shown. The weightings for the Preferreds Blended Index are as follows: 50% BofA Merrill Lynch Fixed Rate Preferred Securities Index and 50% BofA Merrill Lynch U.S. Capital Securities Index.
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 One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown for Class A shares only and would be different for the other share classes.
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. After-tax returns are shown for Class A shares only and would be different for the other share classes.
Performance of a blended index shows how the Fund's performance compares to a blend of indices with similar investment objectives. Performance of the components of the blended index are also shown. The weightings for the Preferreds Blended Index are as follows: 50% BofA Merrill Lynch Fixed Rate Preferred Securities Index and 50% BofA Merrill Lynch U.S. Capital Securities Index. The custom or blended index returns reflect the allocation in effect for the time period(s) for which fund returns are disclosed. Previous weightings or allocations of the custom or blended index are not restated.
Effective January 1, 2017, the Fund’s primary benchmark changed from the BofA Merrill Lynch Fixed Rate Preferred Securities Index to the BofA Merrill Lynch U.S. All Capital Securities Index because the BofA Merrill Lynch U.S. All Capital Securities Index more closely aligns with the Fund’s investments.
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns For the periods ended 12/31/2015
Preferred Securities Fund [Member] | BofA Merrill Lynch U.S. All Capital Securities Index  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses, or taxes)
1 Year rr_AverageAnnualReturnYear01 5.43%
Preferred Securities Fund [Member] | BofA Merrill Lynch Fixed Rate Preferred Securities Index [Member]  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses, or taxes)
1 Year rr_AverageAnnualReturnYear01 7.58%
5 Years rr_AverageAnnualReturnYear05 7.19%
10 Years rr_AverageAnnualReturnYear10 3.30%
Preferred Securities Fund [Member] | BofA Merrill Lynch U.S. Capital Securities Index [Member]  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses, or taxes)
1 Year rr_AverageAnnualReturnYear01 0.86%
5 Years rr_AverageAnnualReturnYear05 7.02%
10 Years rr_AverageAnnualReturnYear10 5.24%
Preferred Securities Fund [Member] | Preferreds Blended Index [Member]  
Prospectus: rr_ProspectusTable  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses, or taxes)
1 Year rr_AverageAnnualReturnYear01 4.18%
5 Years rr_AverageAnnualReturnYear05 7.32%
10 Years rr_AverageAnnualReturnYear10 4.12%
Preferred Securities Fund [Member] | Class A [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 0.76%
5 Years rr_AverageAnnualReturnYear05 6.45%
10 Years rr_AverageAnnualReturnYear10 5.82%
Preferred Securities Fund [Member] | Class A [Member] | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 (1.07%)
5 Years rr_AverageAnnualReturnYear05 4.26%
10 Years rr_AverageAnnualReturnYear10 3.70%
Preferred Securities Fund [Member] | Class A [Member] | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 1.03%
5 Years rr_AverageAnnualReturnYear05 4.31%
10 Years rr_AverageAnnualReturnYear10 3.79%
Preferred Securities Fund [Member] | Class C [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 2.83%
5 Years rr_AverageAnnualReturnYear05 6.48%
10 Years rr_AverageAnnualReturnYear10 5.42%
Preferred Securities Fund [Member] | Class J [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 3.58%
5 Years rr_AverageAnnualReturnYear05 7.10%
10 Years rr_AverageAnnualReturnYear10 5.90%
Preferred Securities Fund [Member] | Class P [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 4.87%
5 Years rr_AverageAnnualReturnYear05 7.54%
10 Years rr_AverageAnnualReturnYear10 6.39%
Preferred Securities Fund [Member] | Institutional Class [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 5.04%
5 Years rr_AverageAnnualReturnYear05 7.62%
10 Years rr_AverageAnnualReturnYear10 6.54%
Preferred Securities Fund [Member] | Class R-1 [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 4.12%
5 Years rr_AverageAnnualReturnYear05 6.72%
10 Years rr_AverageAnnualReturnYear10 5.63%
Preferred Securities Fund [Member] | Class R-2 [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 4.26%
5 Years rr_AverageAnnualReturnYear05 6.87%
10 Years rr_AverageAnnualReturnYear10 5.77%
Preferred Securities Fund [Member] | Class R-3 [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 4.33%
5 Years rr_AverageAnnualReturnYear05 7.04%
10 Years rr_AverageAnnualReturnYear10 5.96%
Preferred Securities Fund [Member] | Class R-4 [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 4.54%
5 Years rr_AverageAnnualReturnYear05 7.22%
10 Years rr_AverageAnnualReturnYear10 6.14%
Preferred Securities Fund [Member] | Class R-5 [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 4.75%
5 Years rr_AverageAnnualReturnYear05 7.40%
10 Years rr_AverageAnnualReturnYear10 6.29%
Preferred Securities Fund [Member] | Class R-6 [Member]  
Prospectus: rr_ProspectusTable  
1 Year rr_AverageAnnualReturnYear01 4.94%
5 Years rr_AverageAnnualReturnYear05 7.51%
10 Years rr_AverageAnnualReturnYear10 6.43%