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Stock-Based Compensation Plans (Details) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended 111 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2015
May 20, 2014
Stock-Based Compensation Plans        
Stock-Based Compensation Plans - Disclosures        
Compensation cost $ 18.4us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansMember
$ 16.8us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansMember
   
Related income tax benefit 6.0us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansMember
5.7us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansMember
   
Capitalized as part of an asset $ 0.7pfg_ShareBasedCompensationArrangementShareBasedPaymentAwardAmountCapitalized
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansMember
$ 0.7pfg_ShareBasedCompensationArrangementShareBasedPaymentAwardAmountCapitalized
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansMember
   
2014 Stock Incentive Plan and 2014 Directors Stock Plan        
Stock-Based Compensation Plans - Disclosures        
Maximum number of new shares of common stock available for grant (in shares) 12,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= pfg_StockIncentivePlansMember
  12,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= pfg_StockIncentivePlansMember
 
Stock Incentive Plan, Directors Stock Plan and Long-Term Performance Plan        
Stock-Based Compensation Plans - Disclosures        
Options granted (in shares)     0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansStockIncentivePlanDirectorsStockPlanLongTermPerformancePlanMember
 
Awards or units granted (in shares)     0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansStockIncentivePlanDirectorsStockPlanLongTermPerformancePlanMember
 
Amended and Restated 2010 Stock Incentive Plan and 2005 Directors Stock Plan        
Stock-Based Compensation Plans - Disclosures        
Number of shares that will be granted       0pfg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesThatWillBeGranted
/ us-gaap_PlanNameAxis
= pfg_StockBasedCompensationPlansAmendedAndRestated2010StockIncentivePlan2005DirectorsStockPlanMember