1.0.0.3 true Consolidated Statements of Stockholders' Equity (USD $) In Millions false 1 $ true false false false Series A us-gaap_StatementClassOfStockAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SeriesAPreferredStockMember us-gaap_StatementClassOfStockAxis explicitMember false false preferred stock us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_PreferredStockMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 2 $ true false false false Series B us-gaap_StatementClassOfStockAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_SeriesBPreferredStockMember us-gaap_StatementClassOfStockAxis explicitMember false false preferred stock us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_PreferredStockMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 3 $ true false false false Common stock us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 4 $ true false false false Additional paid-in capital us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AdditionalPaidInCapitalMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 5 $ true false false false Retained earnings us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_RetainedEarningsMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 6 $ true false false false Accumulated other comprehensive income (loss) us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AccumulatedOtherComprehensiveIncomeMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 7 $ true false false false Treasury stock us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_TreasuryStockMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 8 $ true false false false Noncontrolling interest us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_NoncontrollingInterestMember us-gaap_StatementEquityComponentsAxis explicitMember USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 9 $ false false USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 USDPerShare Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 5 Balances at Dec. 31, 2006 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false true false false 1 true true 0 0 true false 2 true true 100000 0.1 true false 3 true true 3800000 3.8 true false 4 true true 8141800000 8141.8 true false 5 true true 2824100000 2824.1 true false 6 true true 846900000 846.9 true false 7 true true -3955900000 -3955.9 true false 8 true true 58800000 58.8 true false 9 true true 7919600000 7919.6 false false No definition available. No authoritative reference available. false 6 Common stock issued 3 us-gaap_StockIssuedDuringPeriodValueNewIssues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 100000 0.1 true false 4 false true 73500000 73.5 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 73600000 73.6 false false No definition available. No authoritative reference available. false 7 Capital transactions of equity method investee, net of related income taxes 3 pfg_AdjustmentsToAdditionalPaidInCapitalCapitalTransactionsOfEquityMethodInvesteeNetOfTax pfg false credit duration monetary Adjustments to Additional Paid-in Capital due to the capital transactions of equity method investees, net of tax. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true 1100000 1.1 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 1100000 1.1 false false Adjustments to Additional Paid-in Capital due to the capital transactions of equity method investees, net of tax. No authoritative reference available. false 8 Stock-based compensation and additional related tax benefits 3 pfg_ShareBasedCompensationIncludingTaxEffect pfg false credit duration monetary The adjustments to additional paid-in capital during the period associated with equity-based awards as a result of any... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true 79000000 79.0 true false 5 false true -1500000 -1.5 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 77500000 77.5 false false The adjustments to additional paid-in capital during the period associated with equity-based awards as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP), including the tax benefit associated with that plan. This item also includes the impact of common stock dividend equivalents earned on certain unvested equity-based awards, which are charged to retained earnings. No authoritative reference available. false 9 Treasury stock acquired, common 3 us-gaap_TreasuryStockValueAcquiredCostMethod us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true -756300000 -756.3 true false 8 false false 0 0 true false 9 false true -756300000 -756.3 false false No definition available. No authoritative reference available. false 10 Dividends to common stockholders 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -235600000 -235.6 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -235600000 -235.6 false false No definition available. No authoritative reference available. false 11 Dividends to preferred stockholders 3 us-gaap_DividendsPreferredStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -33000000 -33.0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -33000000 -33.0 false false No definition available. No authoritative reference available. false 12 Distributions to noncontrolling interest 3 us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true -13400000 -13.4 true false 9 false true -13400000 -13.4 false false No definition available. No authoritative reference available. false 14 Contributions from noncontrolling interest 3 pfg_CapitalReceivedFromPaidToNoncontrollingInterest pfg false credit duration monetary The net inflow (outflow) from noncontrolling interest to increase or decrease the number of shares they have in the entity.... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 27400000 27.4 true false 9 false true 27400000 27.4 false false The net inflow (outflow) from noncontrolling interest to increase or decrease the number of shares they have in the entity. This does not include dividends paid to minority shareholders. No authoritative reference available. false 17 Comprehensive income (loss): 3 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false false 0 0 false false No definition available. false 18 Net income 4 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 860300000 860.3 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 24200000 24.2 true false 9 false true 884500000 884.5 false false No definition available. No authoritative reference available. false 19 Net unrealized gains (losses), net 4 pfg_OtherComprehensiveIncomeUnrealizedGainLossAdjustmentNetOfTax pfg false credit duration monetary Appreciation or loss in value (after reclassification adjustment) of the total of unsold securities during the period being... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -541900000 -541.9 true false 7 false false 0 0 true false 8 false true -100000 -0.1 true false 9 false true -542000000 -542.0 false false Appreciation or loss in value (after reclassification adjustment) of the total of unsold securities during the period being reported on, net of tax and DAC impacts. Reclassification adjustments include: (1) the unrealized holding gain or loss, net of tax, at the date of the transfer for a debt security from the held-to-maturity category transferred into the available-for-sale category. Also includes the unrealized gain or loss at the date of transfer for a debt security from the available-for-sale category transferred into the held-to-maturity category; (2) the unrealized gains or losses realized upon the sale of securities, after tax; and (3) the unrealized gains or losses realized upon the write-down of securities, after tax. No authoritative reference available. false 21 Foreign currency translation adjustment, net of related income taxes 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 62500000 62.5 true false 7 false false 0 0 true false 8 false true 700000 0.7 true false 9 false true 63200000 63.2 false false No definition available. No authoritative reference available. false 22 Unrecognized postretirement benefit obligation, net of related income taxes 4 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 52700000 52.7 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 52700000 52.7 false false No definition available. No authoritative reference available. false 23 Comprehensive income (loss) 4 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 458400000 458.4 false false No definition available. No authoritative reference available. true 24 Balances at Dec. 31, 2007 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 false true 0 0 true false 2 false true 100000 0.1 true false 3 false true 3900000 3.9 true false 4 false true 8295400000 8295.4 true false 5 false true 3414300000 3414.3 true false 6 false true 420200000 420.2 true false 7 false true -4712200000 -4712.2 true false 8 false true 97600000 97.6 true false 9 false true 7519300000 7519.3 false false No definition available. No authoritative reference available. false 6 Common stock issued 3 us-gaap_StockIssuedDuringPeriodValueNewIssues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true 36400000 36.4 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 36400000 36.4 false false No definition available. No authoritative reference available. false 7 Capital transactions of equity method investee, net of related income taxes 3 pfg_AdjustmentsToAdditionalPaidInCapitalCapitalTransactionsOfEquityMethodInvesteeNetOfTax pfg false credit duration monetary Adjustments to Additional Paid-in Capital due to the capital transactions of equity method investees, net of tax. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true 600000 0.6 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 600000 0.6 false false Adjustments to Additional Paid-in Capital due to the capital transactions of equity method investees, net of tax. No authoritative reference available. false 8 Stock-based compensation and additional related tax benefits 3 pfg_ShareBasedCompensationIncludingTaxEffect pfg false credit duration monetary The adjustments to additional paid-in capital during the period associated with equity-based awards as a result of any... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true 44100000 44.1 true false 5 false true -1100000 -1.1 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 43000000 43.0 false false The adjustments to additional paid-in capital during the period associated with equity-based awards as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP), including the tax benefit associated with that plan. This item also includes the impact of common stock dividend equivalents earned on certain unvested equity-based awards, which are charged to retained earnings. No authoritative reference available. false 9 Treasury stock acquired, common 3 us-gaap_TreasuryStockValueAcquiredCostMethod us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true -6400000 -6.4 true false 8 false false 0 0 true false 9 false true -6400000 -6.4 false false No definition available. No authoritative reference available. false 10 Dividends to common stockholders 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -116700000 -116.7 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -116700000 -116.7 false false No definition available. No authoritative reference available. false 11 Dividends to preferred stockholders 3 us-gaap_DividendsPreferredStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -33000000 -33.0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -33000000 -33.0 false false No definition available. No authoritative reference available. false 12 Distributions to noncontrolling interest 3 us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true -14600000 -14.6 true false 9 false true -14600000 -14.6 false false No definition available. No authoritative reference available. false 14 Contributions from noncontrolling interest 3 pfg_CapitalReceivedFromPaidToNoncontrollingInterest pfg false credit duration monetary The net inflow (outflow) from noncontrolling interest to increase or decrease the number of shares they have in the entity.... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 7000000 7.0 true false 9 false true 7000000 7.0 false false The net inflow (outflow) from noncontrolling interest to increase or decrease the number of shares they have in the entity. This does not include dividends paid to minority shareholders. No authoritative reference available. false 15 Effects of changing postretirement benefit plan measurement date, net of related income taxes 3 pfg_EffectOfChangingPostRetirementBenefitPlanMeasurementDateNetOfRelatedIncomeTaxes pfg false credit duration monetary Adjustment increasing (decreasing) stockholders' equity due to a change in the measurement date for a defined benefit pension... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 900000 0.9 true false 6 false true -2000000 -2.0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -1100000 -1.1 false false Adjustment increasing (decreasing) stockholders' equity due to a change in the measurement date for a defined benefit pension and other postretirement plan in the initial application of the measurement provisions of SFAS 158. No authoritative reference available. false 17 Comprehensive income (loss): 3 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false false 0 0 false false No definition available. false 18 Net income 4 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 458100000 458.1 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 7700000 7.7 true false 9 false true 465800000 465.8 false false No definition available. No authoritative reference available. false 19 Net unrealized gains (losses), net 4 pfg_OtherComprehensiveIncomeUnrealizedGainLossAdjustmentNetOfTax pfg false credit duration monetary Appreciation or loss in value (after reclassification adjustment) of the total of unsold securities during the period being... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -4487900000 -4487.9 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -4487900000 -4487.9 false false Appreciation or loss in value (after reclassification adjustment) of the total of unsold securities during the period being reported on, net of tax and DAC impacts. Reclassification adjustments include: (1) the unrealized holding gain or loss, net of tax, at the date of the transfer for a debt security from the held-to-maturity category transferred into the available-for-sale category. Also includes the unrealized gain or loss at the date of transfer for a debt security from the available-for-sale category transferred into the held-to-maturity category; (2) the unrealized gains or losses realized upon the sale of securities, after tax; and (3) the unrealized gains or losses realized upon the write-down of securities, after tax. No authoritative reference available. false 21 Foreign currency translation adjustment, net of related income taxes 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -209400000 -209.4 true false 7 false false 0 0 true false 8 false true -1200000 -1.2 true false 9 false true -210600000 -210.6 false false No definition available. No authoritative reference available. false 22 Unrecognized postretirement benefit obligation, net of related income taxes 4 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -632500000 -632.5 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -632500000 -632.5 false false No definition available. No authoritative reference available. false 23 Comprehensive income (loss) 4 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -4865200000 -4865.2 false false No definition available. No authoritative reference available. true 24 Balances at Dec. 31, 2008 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 false true 0 0 true false 2 false true 100000 0.1 true false 3 false true 3900000 3.9 true false 4 false true 8376500000 8376.5 true false 5 false true 3722500000 3722.5 true false 6 false true -4911600000 -4911.6 true false 7 false true -4718600000 -4718.6 true false 8 false true 96500000 96.5 true false 9 false true 2569300000 2569.3 false false No definition available. No authoritative reference available. false 6 Common stock issued 3 us-gaap_StockIssuedDuringPeriodValueNewIssues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 600000 0.6 true false 4 false true 1122400000 1122.4 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 1123000000 1123.0 false false No definition available. No authoritative reference available. false 8 Stock-based compensation and additional related tax benefits 3 pfg_ShareBasedCompensationIncludingTaxEffect pfg false credit duration monetary The adjustments to additional paid-in capital during the period associated with equity-based awards as a result of any... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true 39900000 39.9 true false 5 false true -1900000 -1.9 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 38000000 38.0 false false The adjustments to additional paid-in capital during the period associated with equity-based awards as a result of any share-based compensation plan other than an employee stock ownership plan (ESOP), including the tax benefit associated with that plan. This item also includes the impact of common stock dividend equivalents earned on certain unvested equity-based awards, which are charged to retained earnings. No authoritative reference available. false 9 Treasury stock acquired, common 3 us-gaap_TreasuryStockValueAcquiredCostMethod us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false true -4100000 -4.1 true false 8 false false 0 0 true false 9 false true -4100000 -4.1 false false No definition available. No authoritative reference available. false 10 Dividends to common stockholders 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -159500000 -159.5 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -159500000 -159.5 false false No definition available. No authoritative reference available. false 11 Dividends to preferred stockholders 3 us-gaap_DividendsPreferredStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true -33000000 -33.0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -33000000 -33.0 false false No definition available. No authoritative reference available. false 12 Distributions to noncontrolling interest 3 us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true -7100000 -7.1 true false 9 false true -7100000 -7.1 false false No definition available. No authoritative reference available. false 13 Purchase of subsidiary shares from noncontrolling interest 3 us-gaap_MinorityInterestDecreaseFromRedemptions us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true -45900000 -45.9 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 200000 0.2 true false 9 false true -45700000 -45.7 false false No definition available. No authoritative reference available. false 14 Contributions from noncontrolling interest 3 pfg_CapitalReceivedFromPaidToNoncontrollingInterest pfg false credit duration monetary The net inflow (outflow) from noncontrolling interest to increase or decrease the number of shares they have in the entity.... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 10100000 10.1 true false 9 false true 10100000 10.1 false false The net inflow (outflow) from noncontrolling interest to increase or decrease the number of shares they have in the entity. This does not include dividends paid to minority shareholders. No authoritative reference available. false 16 Effects of reclassifying noncredit component of previously recognized impairment losses on fixed maturities, available-for-sale, net 3 pfg_EffectsOfReclassifyingNoncreditComponentOfPreviouslyRecognizedImpairmentLossesOnFixedMaturitiesAvailableForSaleNet pfg false credit duration monetary This item represents the after-tax reclassification of noncredit impairment losses, net of assumed changes in amortization... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 9900000 9.9 true false 6 false true -9900000 -9.9 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false false 0 0 false false This item represents the after-tax reclassification of noncredit impairment losses, net of assumed changes in amortization patterns, for certain debt securities impaired prior to the adoption of new accounting guidance that allows the bifurcation of other-than-temporary impairments between credit losses recognized in the income statement and noncredit losses recognized in other comprehensive income. No authoritative reference available. false 17 Comprehensive income (loss): 3 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false false 0 0 false false No definition available. false 18 Net income 4 us-gaap_ProfitLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false true 622700000 622.7 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false true 23000000 23.0 true false 9 false true 645700000 645.7 false false No definition available. No authoritative reference available. false 19 Net unrealized gains (losses), net 4 pfg_OtherComprehensiveIncomeUnrealizedGainLossAdjustmentNetOfTax pfg false credit duration monetary Appreciation or loss in value (after reclassification adjustment) of the total of unsold securities during the period being... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 3693100000 3693.1 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 3693100000 3693.1 false false Appreciation or loss in value (after reclassification adjustment) of the total of unsold securities during the period being reported on, net of tax and DAC impacts. Reclassification adjustments include: (1) the unrealized holding gain or loss, net of tax, at the date of the transfer for a debt security from the held-to-maturity category transferred into the available-for-sale category. Also includes the unrealized gain or loss at the date of transfer for a debt security from the available-for-sale category transferred into the held-to-maturity category; (2) the unrealized gains or losses realized upon the sale of securities, after tax; and (3) the unrealized gains or losses realized upon the write-down of securities, after tax. No authoritative reference available. false 20 Noncredit component of impairment losses on fixed maturities, available-for-sale, net 4 pfg_OtherComprehensiveIncomeReclassificationAdjustmentNetOfTax pfg false credit duration monetary Noncredit portion of impairment losses on debt securities for the period that meet the criteria to have impairment losses... false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true -152900000 -152.9 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true -152900000 -152.9 false false Noncredit portion of impairment losses on debt securities for the period that meet the criteria to have impairment losses bifurcated between net income (credit losses) and OCI (noncredit losses), net of related taxes and assumed changes in amortization patterns. No authoritative reference available. false 21 Foreign currency translation adjustment, net of related income taxes 4 us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 168200000 168.2 true false 7 false false 0 0 true false 8 false true 200000 0.2 true false 9 false true 168400000 168.4 false false No definition available. No authoritative reference available. false 22 Unrecognized postretirement benefit obligation, net of related income taxes 4 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false true 171100000 171.1 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 171100000 171.1 false false No definition available. No authoritative reference available. false 23 Comprehensive income (loss) 4 us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 true false 6 false false 0 0 true false 7 false false 0 0 true false 8 false false 0 0 true false 9 false true 4525400000 4525.4 false false No definition available. No authoritative reference available. true 24 Balances at Dec. 31, 2009 3 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 true true 0 0 true false 2 true true 100000 0.1 true false 3 true true 4500000 4.5 true false 4 true true 9492900000 9492.9 true false 5 true true 4160700000 4160.7 true false 6 true true -1042000000 -1042.0 true false 7 true true -4722700000 -4722.7 true false 8 true true 122900000 122.9 true false 9 true true 8016400000 8016.4 false false No definition available. No authoritative reference available. false false 9 49 false HundredThousands UnKnown UnKnown false true