1.0.0.3 true Consolidated Statements of Financial Position (USD $) In Millions false 1 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 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 false 2 $ false false Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 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 2 Assets 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 3 Fixed maturities, available-for-sale 2 us-gaap_AvailableForSaleSecuritiesDebtSecurities us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 true true 46220600000 46220.6 false false 2 true true 40117200000 40117.2 false false No definition available. No authoritative reference available. false 4 Fixed maturities, trading 2 us-gaap_TradingSecuritiesDebt us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1032400000 1032.4 false false 2 false true 843400000 843.4 false false No definition available. No authoritative reference available. false 5 Equity securities, available-for-sale 2 us-gaap_AvailableForSaleSecuritiesEquitySecurities us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 214000000 214.0 false false 2 false true 242700000 242.7 false false No definition available. No authoritative reference available. false 6 Equity securities, trading 2 us-gaap_TradingSecuritiesEquity us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 221500000 221.5 false false 2 false true 158000000 158.0 false false No definition available. No authoritative reference available. false 7 Mortgage loans 2 us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 11845600000 11845.6 false false 2 false true 13113600000 13113.6 false false No definition available. No authoritative reference available. false 8 Real estate 2 pfg_InvestmentsInRealEstate pfg false debit instant monetary Investments in real estate held for investment purposes and held-for-sale. false false false false false false false false false 1 false true 1034600000 1034.6 false false 2 false true 919400000 919.4 false false Investments in real estate held for investment purposes and held-for-sale. No authoritative reference available. false 9 Policy loans 2 us-gaap_LoansInsurancePolicy us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 902500000 902.5 false false 2 false true 896400000 896.4 false false No definition available. No authoritative reference available. false 10 Other investments 2 pfg_OtherInvestmentsAsDefined pfg false debit instant monetary Other investments include, but are not limited to, derivative assets, noncontrolling interests in subsidiaries and real... false false false false false false false false false 1 false true 2465300000 2465.3 false false 2 false true 2816600000 2816.6 false false Other investments include, but are not limited to, derivative assets, noncontrolling interests in subsidiaries and real estate and company's ownership in corporate sponsored mutual funds. No authoritative reference available. false 11 Total investments 2 us-gaap_Investments us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 63936500000 63936.5 false false 2 false true 59107300000 59107.3 false false No definition available. No authoritative reference available. true 12 Cash and cash equivalents 2 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 2240400000 2240.4 false false 2 false true 2608000000 2608.0 false false No definition available. No authoritative reference available. false 13 Accrued investment income 2 us-gaap_AccruedInvestmentIncomeReceivable us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 691900000 691.9 false false 2 false true 750700000 750.7 false false No definition available. No authoritative reference available. false 14 Premiums due and other receivables 2 us-gaap_PremiumsAndOtherReceivablesNet us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1065400000 1065.4 false false 2 false true 988100000 988.1 false false No definition available. No authoritative reference available. false 15 Deferred policy acquisition costs 2 us-gaap_DeferredPolicyAcquisitionCosts us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 3681400000 3681.4 false false 2 false true 4153000000 4153.0 false false No definition available. No authoritative reference available. false 16 Property and equipment 2 pfg_PropertyAndEquipment pfg false debit instant monetary Tangible assets that are held by an entity for use in the production or supply of goods and services, for rental to others,... false false false false false false false false false 1 false true 489300000 489.3 false false 2 false true 518200000 518.2 false false Tangible assets that are held by an entity for use in the production or supply of goods and services, for rental to others, or for administrative purposes and that are expected to provide economic benefit for more than one year and intangible assets for software; net of accumulated depreciation. Examples of tangible assets include land, buildings and equipment. No authoritative reference available. false 17 Goodwill 2 us-gaap_Goodwill us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 386400000 386.4 false false 2 false true 375500000 375.5 false false No definition available. No authoritative reference available. false 18 Other intangibles 2 us-gaap_IntangibleAssetsNetExcludingGoodwill us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 851700000 851.7 false false 2 false true 925300000 925.3 false false No definition available. No authoritative reference available. false 19 Separate account assets 2 us-gaap_SeparateAccountAssets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 62738500000 62738.5 false false 2 false true 55142600000 55142.6 false false No definition available. No authoritative reference available. false 20 Other assets 2 us-gaap_OtherAssets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 1677900000 1677.9 false false 2 false true 3613700000 3613.7 false false No definition available. No authoritative reference available. false 21 Total assets 2 us-gaap_Assets us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true 137759400000 137759.4 false false 2 false true 128182400000 128182.4 false false No definition available. No authoritative reference available. true 22 Liabilities 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 23 Contractholder funds 2 pfg_ContractholderFunds pfg false credit instant monetary Contractholder funds include reserves for investment-type insurance contracts and reserves for universal life insurance. false false false false false false false false false 1 false true 39801900000 39801.9 false false 2 false true 43086600000 43086.6 false false Contractholder funds include reserves for investment-type insurance contracts and reserves for universal life insurance. No authoritative reference available. false 24 Future policy benefits and claims 2 us-gaap_LiabilityForFuturePolicyBenefitsAndUnpaidClaimsAndClaimsAdjustmentExpense us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 19248300000 19248.3 false false 2 false true 18494200000 18494.2 false false No definition available. No authoritative reference available. false 25 Other policyholder funds 2 us-gaap_OtherPolicyholderFunds us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 559200000 559.2 false false 2 false true 536200000 536.2 false false No definition available. No authoritative reference available. false 26 Short-term debt 2 us-gaap_ShortTermBorrowings us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 101600000 101.6 false false 2 false true 500900000 500.9 false false No definition available. No authoritative reference available. false 27 Long-term debt 2 us-gaap_LongTermDebt us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 1584600000 1584.6 false false 2 false true 1290500000 1290.5 false false No definition available. No authoritative reference available. false 28 Income taxes currently payable 2 us-gaap_AccruedIncomeTaxes us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 2800000 2.8 false false 2 false true 1900000 1.9 false false No definition available. No authoritative reference available. false 29 Deferred income taxes 2 us-gaap_DeferredIncomeTaxLiabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 120200000 120.2 false false 2 false true 102800000 102.8 false false No definition available. No authoritative reference available. false 30 Separate account liabilities 2 us-gaap_SeparateAccountsLiability us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 62738500000 62738.5 false false 2 false true 55142600000 55142.6 false false No definition available. No authoritative reference available. false 31 Other liabilities 2 us-gaap_OtherLiabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 5585900000 5585.9 false false 2 false true 6457400000 6457.4 false false No definition available. No authoritative reference available. false 32 Total liabilities 2 us-gaap_Liabilities us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 129743000000 129743.0 false false 2 false true 125613100000 125613.1 false false No definition available. No authoritative reference available. true 33 Stockholders' equity 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 35 Common stock, par value $.01 per share - 2,500.0 million shares authorized, 447.0 million and 387.0 million shares issued, and 319.0 million and 259.3 million shares outstanding at December 31, 2009 and 2008, respectively 2 us-gaap_CommonStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 4500000 4.5 false false 2 false true 3900000 3.9 false false No definition available. No authoritative reference available. false 36 Additional paid-in capital 2 us-gaap_AdditionalPaidInCapital us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 9492900000 9492.9 false false 2 false true 8376500000 8376.5 false false No definition available. No authoritative reference available. false 37 Retained earnings 2 us-gaap_RetainedEarningsAccumulatedDeficit us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 4160700000 4160.7 false false 2 false true 3722500000 3722.5 false false No definition available. No authoritative reference available. false 38 Accumulated other comprehensive loss 2 us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true -1042000000 -1042.0 false false 2 false true -4911600000 -4911.6 false false No definition available. No authoritative reference available. false 39 Treasury stock, at cost (128.0 million and 127.7 million shares at December 31, 2009 and 2008, respectively) 2 us-gaap_TreasuryStockValue us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false true -4722700000 -4722.7 false false 2 false true -4718600000 -4718.6 false false No definition available. No authoritative reference available. false 40 Total stockholders' equity attributable to Principal Financial Group, Inc. 2 us-gaap_StockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 7893500000 7893.5 false false 2 false true 2472800000 2472.8 false false No definition available. No authoritative reference available. true 41 Noncontrolling interest 2 us-gaap_MinorityInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 122900000 122.9 false false 2 false true 96500000 96.5 false false No definition available. No authoritative reference available. false 42 Total stockholders' equity 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 8016400000 8016.4 false false 2 false true 2569300000 2569.3 false false No definition available. No authoritative reference available. true 43 Total liabilities and stockholders' equity 2 us-gaap_LiabilitiesAndStockholdersEquity us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 137759400000 137759.4 false false 2 false true 128182400000 128182.4 false false No definition available. No authoritative reference available. true 44 Series A 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 76 Stockholders' equity 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 77 Preferred stock, value 2 us-gaap_PreferredStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false No definition available. No authoritative reference available. false 87 Series A | preferred stock 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 119 Stockholders' equity 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 128 Total stockholders' equity 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true 0 0 false false No definition available. No authoritative reference available. true 130 Series B 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 162 Stockholders' equity 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 163 Preferred stock, value 2 us-gaap_PreferredStockValue us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false true 100000 0.1 false false 2 false true 100000 0.1 false false No definition available. No authoritative reference available. false 173 Series B | preferred stock 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 205 Stockholders' equity 2 us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. false 214 Total stockholders' equity 2 us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 true true 100000 0.1 false false 2 true true 100000 0.1 false false No definition available. No authoritative reference available. true false 2 53 false HundredThousands UnKnown UnKnown false true