Name:	pfg_AccumulatedOtherComprehensiveIncomeLossOtherThanTemporaryImpairmentNotCreditLossAvailableForSaleDebtSecurities
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the cumulative net unrealized gains/losses adjustment related to deferred policy acquisition costs, sales inducements and unearned revenue reserves.

No definition available.

Name:	pfg_AdjustmentsAssumedChangesAmortizationPatterns
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the cumulative net unrealized gains/losses adjustment related to changes in policyholder benefits and claims and changes in the policyholder dividend obligation.

No definition available.

Name:	pfg_AdjustmentsAssumedChangesLiabilityForPolicyholderBenefitsAndClaims
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the balance sheet side of the after-tax impact resulting from the adoption of new embedded credit derivative accounting guidance and represents the unrealized losses, net of assumed changes in amortization patterns, on fixed maturities for which the fair value option was elected, effectively reclassifying them from available-for-sale to trading.

No definition available.

Name:	pfg_EffectsOfImplementationOfAccountingChangeRelatedToEmbeddedCreditDerivativesNetBalanceSheet
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the balance sheet side of the after-tax impact resulting from the adoption of new variable interest entities accounting guidance and consists of (a) the difference between the net amount added to the consolidated balance sheet and the amount of any previously recognized interest in newly consolidated variable interest entities and (b) the difference between the net amount removed from the consolidated balance sheet and the amount of any retained interest in newly deconsolidated variable interest entities.

No definition available.

Name:	pfg_EffectsOfImplementationOfAccountingChangeRelatedToVariableInterestEntitiesNetBalanceSheet
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The cumulative net unrealized gains/losses on fixed maturities available-for-sale, equity securities available-for-sale and derivative instruments net of adjustments related to deferred policy acquisition costs, sales inducements, unearned revenue reserves, changes in policyholder benefits and claims and applicable income taxes.

No definition available.

Name:	pfg_NetUnrealizedGainsLossesAvailableForSaleSecuritiesAndDerivativeInstruments
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	pfg_NetUnrealizedGainsLossesAvailableForSaleSecuritiesAndDerivativeInstrumentsAbstract
Namespace Prefix:	pfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This item represents the cumulative net unrealized gains and losses on fixed maturities available-for-sale, excluding hedged portions of those in fair value hedging.

No definition available.

Name:	pfg_NetUnrealizedGainsLossesDebtSecuritiesAvailableForSaleSecurities
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the cumulative net unrealized gains/losses on derivatives in qualifying cash flow hedges.

No definition available.

Name:	pfg_NetUnrealizedGainsLossesDerivativeInstruments
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the cumulative net unrealized gains/losses on investments in our subsidiaries, which represents the difference between the market value and original cost of the investment in the subsidiary.

No definition available.

Name:	pfg_NetUnrealizedGainsLossesEquityMethodSubsidiariesAndNoncontrollingInterestAdjustments
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the cumulative net unrealized gains/losses for equity securities available-for-sale.

No definition available.

Name:	pfg_NetUnrealizedGainsLossesEquitySecuritiesAvailableForSale
Namespace Prefix:	pfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

This item represents the applicable deferred income tax impacts of cumulative net unrealized gains/losses on fixed maturities available-for-sale, equity securities available-for-sale and derivative instruments net of adjustments related deferred policy acquisition costs, sales inducements, unearned revenue reserves, and changes in policyholder benefits and claims.

No definition available.