XML 161 R69.htm IDEA: XBRL DOCUMENT v2.4.1.9
Investments (Details 9) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Mortgage loan disclosures        
Mortgage loans, Total amortized cost $ 11,868.1us-gaap_NotesReceivableGross $ 11,603.4us-gaap_NotesReceivableGross $ 11,617.1us-gaap_NotesReceivableGross  
Mortgage loan valuation allowance (56.5)us-gaap_FinancingReceivableAllowanceForCreditLosses (69.8)us-gaap_FinancingReceivableAllowanceForCreditLosses (97.4)us-gaap_FinancingReceivableAllowanceForCreditLosses (102.1)us-gaap_FinancingReceivableAllowanceForCreditLosses
Mortgage loans, Total carrying value 11,811.6us-gaap_NotesReceivableNet 11,533.6us-gaap_NotesReceivableNet    
Commercial mortgage loans        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 10,723.8us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
10,327.7us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
10,235.1us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
 
Mortgage loan valuation allowance (26.9)us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
(28.7)us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
(51.8)us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
(64.8)us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Mortgage loans, purchased 59.5us-gaap_FinancingReceivableSignificantPurchases
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
166.1us-gaap_FinancingReceivableSignificantPurchases
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
149.1us-gaap_FinancingReceivableSignificantPurchases
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
 
Mortgage loans, sold 2.3us-gaap_FinancingReceivableSignificantSales
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
13.0us-gaap_FinancingReceivableSignificantSales
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
31.1us-gaap_FinancingReceivableSignificantSales
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
 
Percent of mortgage loans (as a percent) 100.00%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
100.00%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Commercial mortgage loans | Office        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 3,646.1us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
3,360.5us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Percent of mortgage loans (as a percent) 34.00%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
32.60%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Commercial mortgage loans | Retail        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 2,512.1us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
2,668.5us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Percent of mortgage loans (as a percent) 23.40%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
25.80%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Commercial mortgage loans | Industrial        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 1,918.7us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
1,766.2us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Percent of mortgage loans (as a percent) 17.90%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
17.10%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Commercial mortgage loans | Apartments        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 2,200.5us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_ApartmentBuildingMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
1,911.2us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_ApartmentBuildingMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Percent of mortgage loans (as a percent) 20.50%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_ApartmentBuildingMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
18.50%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_ApartmentBuildingMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Commercial mortgage loans | Hotel        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 331.5us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_HotelMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
333.1us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_HotelMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Percent of mortgage loans (as a percent) 3.10%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_HotelMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
3.20%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_HotelMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Commercial mortgage loans | Mixed use/other        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 114.9us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OtherPropertyMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
288.2us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OtherPropertyMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Percent of mortgage loans (as a percent) 1.10%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OtherPropertyMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
2.80%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OtherPropertyMember
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
   
Commercial mortgage loans | New England        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 528.0us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_NewEnglandMember
528.5us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_NewEnglandMember
   
Percent of mortgage loans (as a percent) 4.90%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_NewEnglandMember
5.10%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_NewEnglandMember
   
Commercial mortgage loans | Middle Atlantic        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 2,951.0us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_MiddleAtlanticMember
2,489.0us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_MiddleAtlanticMember
   
Percent of mortgage loans (as a percent) 27.50%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_MiddleAtlanticMember
24.10%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_MiddleAtlanticMember
   
Commercial mortgage loans | East North Central        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 442.1us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_EastNorthCentralMember
519.9us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_EastNorthCentralMember
   
Percent of mortgage loans (as a percent) 4.10%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_EastNorthCentralMember
5.00%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_EastNorthCentralMember
   
Commercial mortgage loans | West North Central        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 233.3us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_WestNorthCentralMember
302.9us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_WestNorthCentralMember
   
Percent of mortgage loans (as a percent) 2.20%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_WestNorthCentralMember
2.90%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_WestNorthCentralMember
   
Commercial mortgage loans | South Atlantic        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 1,970.9us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_SouthAtlanticMember
1,949.5us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_SouthAtlanticMember
   
Percent of mortgage loans (as a percent) 18.40%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_SouthAtlanticMember
18.90%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_SouthAtlanticMember
   
Commercial mortgage loans | East South Central        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 197.4us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_EastSouthCentralMember
192.8us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_EastSouthCentralMember
   
Percent of mortgage loans (as a percent) 1.80%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_EastSouthCentralMember
1.90%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_EastSouthCentralMember
   
Commercial mortgage loans | West South Central        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 1,023.9us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_WestSouthCentralMember
830.3us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_WestSouthCentralMember
   
Percent of mortgage loans (as a percent) 9.50%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_WestSouthCentralMember
8.00%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_WestSouthCentralMember
   
Commercial mortgage loans | Mountain        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 772.0us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_MountainMember
747.1us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_MountainMember
   
Percent of mortgage loans (as a percent) 7.20%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_MountainMember
7.20%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_MountainMember
   
Commercial mortgage loans | Pacific        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 2,565.5us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_PacificMember
2,722.5us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_PacificMember
   
Percent of mortgage loans (as a percent) 24.00%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_PacificMember
26.50%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_PacificMember
   
Commercial mortgage loans | International        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 39.7us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_InternationalMember
45.2us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_InternationalMember
   
Percent of mortgage loans (as a percent) 0.40%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_InternationalMember
0.40%pfg_PercentageOfMortgageLoans
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
/ us-gaap_StatementGeographicalAxis
= pfg_InternationalMember
   
Residential mortgage loans        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 1,144.3us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
1,275.7us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
1,382.0us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
 
Mortgage loan valuation allowance (29.6)us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
(41.1)us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
(45.6)us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
(37.3)us-gaap_FinancingReceivableAllowanceForCreditLosses
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
Mortgage loans, purchased 184.8us-gaap_FinancingReceivableSignificantPurchases
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
157.2us-gaap_FinancingReceivableSignificantPurchases
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
153.0us-gaap_FinancingReceivableSignificantPurchases
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
 
Mortgage loans, sold 95.9us-gaap_FinancingReceivableSignificantSales
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
0us-gaap_FinancingReceivableSignificantSales
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
14.2us-gaap_FinancingReceivableSignificantSales
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_ResidentialMortgageMember
 
Home equity        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost 283.4us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_HomeEquityMember
394.9us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_HomeEquityMember
   
First liens        
Mortgage loan disclosures        
Mortgage loans, Total amortized cost $ 860.9us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_FirstMortgageMember
$ 880.8us-gaap_NotesReceivableGross
/ us-gaap_MortgageLoansOnRealEstateLoanTypeAxis
= us-gaap_FirstMortgageMember