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Label Element Value
Prospectus: rr_ProspectusTable  
Document Type dei_DocumentType Other
Document Period End Date dei_DocumentPeriodEndDate Oct. 31, 2015
Entity Registrant Name dei_EntityRegistrantName PRINCIPAL FUNDS INC
Central Index Key dei_EntityCentralIndexKey 0000898745
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Sep. 22, 2016
Document Effective Date dei_DocumentEffectiveDate Sep. 22, 2016
Prospectus Date rr_ProspectusDate Mar. 01, 2016
Supplement [Text Block] ck0000898745_SupplementTextBlock
Principal Funds, Inc.

Supplement dated September 22, 2016
to the Statutory Prospectus dated March 1, 2016
(as supplemented on March 9, 2016, March 18, 2016, May 2, 2016, May 31, 2016,
June 17, 2016, June 30, 2016, July 29, 2016, August 5, 2016, and September 16, 2016)

This supplement updates information currently in the Statutory Prospectus. Please retain this supplement for future reference.
SmallCap Value Fund II [Member]  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading SMALLCAP VALUE FUND II
Performance Table Heading rr_PerformanceTableHeading In the Average Annual Total Returns table, delete the Class A Return rows, and replace with the following:
SmallCap Value Fund II [Member] | SmallCap Value Fund II, Class A  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (9.76%)
5 Years rr_AverageAnnualReturnYear05 7.73%
10 Years rr_AverageAnnualReturnYear10 5.16%
SmallCap Value Fund II [Member] | SmallCap Value Fund II, Class A | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (12.11%)
5 Years rr_AverageAnnualReturnYear05 5.73%
10 Years rr_AverageAnnualReturnYear10 3.45%
SmallCap Value Fund II [Member] | SmallCap Value Fund II, Class A | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return After Taxes on Distribution and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 (3.74%)
5 Years rr_AverageAnnualReturnYear05 5.58%
10 Years rr_AverageAnnualReturnYear10 3.72%
SmallCap Growth Fund I [Member]  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading SMALLCAP GROWTH FUND I
Performance Table Heading rr_PerformanceTableHeading In the Average Annual Total Returns table, delete the Institutional Class Return rows, and replace with the following:
SmallCap Growth Fund I [Member] | SmallCap Growth I Fund, Institutional Class [Member]  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Institutional Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 1.19%
5 Years rr_AverageAnnualReturnYear05 11.11%
10 Years rr_AverageAnnualReturnYear10 8.52%
SmallCap Growth Fund I [Member] | SmallCap Growth I Fund, Institutional Class [Member] | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Institutional Class Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (0.83%)
5 Years rr_AverageAnnualReturnYear05 8.74%
10 Years rr_AverageAnnualReturnYear10 7.12%
SmallCap Growth Fund I [Member] | SmallCap Growth I Fund, Institutional Class [Member] | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Institutional Class Return After Taxes on Distribution and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 2.33%
5 Years rr_AverageAnnualReturnYear05 8.77%
10 Years rr_AverageAnnualReturnYear10 6.89%
SmallCap S&P 600 Index Fund [Member]  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading SMALLCAP S&P 600 INDEX FUND
Performance Table Heading rr_PerformanceTableHeading In the Average Annual Total Returns table, delete the Institutional Class Return rows, and replace with the following:
SmallCap S&P 600 Index Fund [Member] | SmallCap S&P 600 Index Fund, Institutional Class [Member]  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Institutional Class Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (2.22%)
5 Years rr_AverageAnnualReturnYear05 11.20%
10 Years rr_AverageAnnualReturnYear10 7.79%
SmallCap S&P 600 Index Fund [Member] | SmallCap S&P 600 Index Fund, Institutional Class [Member] | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Institutional Class Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (4.40%)
5 Years rr_AverageAnnualReturnYear05 10.02%
10 Years rr_AverageAnnualReturnYear10 6.74%
SmallCap S&P 600 Index Fund [Member] | SmallCap S&P 600 Index Fund, Institutional Class [Member] | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Institutional Class Return After Taxes on Distribution and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 0.04%
5 Years rr_AverageAnnualReturnYear05 8.83%
10 Years rr_AverageAnnualReturnYear10 6.20%
SmallCap Fund (Formerly SmallCap Blend Fund) [Member]  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading SMALLCAP FUND
Performance Table Heading rr_PerformanceTableHeading In the Average Annual Total Returns table, delete the Class A Return rows, and replace with the following:
SmallCap Fund (Formerly SmallCap Blend Fund) [Member] | SmallCap Blend Fund, Class A [Member]  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (5.95%)
5 Years rr_AverageAnnualReturnYear05 10.12%
10 Years rr_AverageAnnualReturnYear10 5.72%
SmallCap Fund (Formerly SmallCap Blend Fund) [Member] | SmallCap Blend Fund, Class A [Member] | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (6.76%)
5 Years rr_AverageAnnualReturnYear05 8.89%
10 Years rr_AverageAnnualReturnYear10 4.84%
SmallCap Fund (Formerly SmallCap Blend Fund) [Member] | SmallCap Blend Fund, Class A [Member] | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return After Taxes on Distribution and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 (2.69%)
5 Years rr_AverageAnnualReturnYear05 7.95%
10 Years rr_AverageAnnualReturnYear10 4.55%
Tax-Exempt Bond Fund [Member]  
Prospectus: rr_ProspectusTable  
Risk/Return [Heading] rr_RiskReturnHeading TAX-EXEMPT BOND FUND
Performance Table Heading rr_PerformanceTableHeading In the Average Annual Total Returns table, delete the Class A Return rows, and replace with the following:
Tax-Exempt Bond Fund [Member] | Tax-Exempt Bond Fund, Class A [Member]  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (0.07%)
5 Years rr_AverageAnnualReturnYear05 5.24%
10 Years rr_AverageAnnualReturnYear10 3.89%
Tax-Exempt Bond Fund [Member] | Tax-Exempt Bond Fund, Class A [Member] | After Taxes on Distributions  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (0.07%)
5 Years rr_AverageAnnualReturnYear05 5.24%
10 Years rr_AverageAnnualReturnYear10 3.89%
Tax-Exempt Bond Fund [Member] | Tax-Exempt Bond Fund, Class A [Member] | After Taxes on Distributions and Sales  
Prospectus: rr_ProspectusTable  
Label rr_AverageAnnualReturnLabel Class A Return After Taxes on Distribution and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 1.55%
5 Years rr_AverageAnnualReturnYear05 5.03%
10 Years rr_AverageAnnualReturnYear10 3.97%