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Fair Value Measurements - Level 3 Inputs Reconciliation (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Fair Value, Level 1 to level 3 Transfers, Amount | $ 0 kmpr_FairValueLevel1ToLevel3TransfersAmount | $ 0 kmpr_FairValueLevel1ToLevel3TransfersAmount
Fair Value, Level 3 to level 1 Transfers, Amount | 0 kmpr_FairValueLevel3ToLevel1TransfersAmount | 0 kmpr_FairValueLevel3ToLevel1TransfersAmount
Fair Value, Level 1 to Level 2 Activity Transfers, Amount | 0 kmpr_FairValueLevel1ToLevel2ActivityTransfersAmount | 0 kmpr_FairValueLevel1ToLevel2ActivityTransfersAmount
Fair Value, Level 2 to Level 1 Activity Transfers, Amount | 0 kmpr_FairValueLevel2ToLevel1ActivityTransfersAmount | 0 kmpr_FairValueLevel2ToLevel1ActivityTransfersAmount
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Balance at Beginning of Year | 626,700,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue | 520,400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Included in Consolidated Statement of Income | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 | (10,000,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
Included in Other Comprehensive Income | 6,800,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss | 1,000,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss
Purchases | 347,400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases | 270,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Settlements | (172,100,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements | (151,400,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Sales | (96,600,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales | (2,800,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Transfers Into Level 3 | 3,600,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 | 8,200,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
Transfers out of Level 3 | (1,900,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 | (8,800,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Balance at End of Year | 713,900,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue | 626,700,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Corporate Bonds and Notes [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Balance at Beginning of Year | 364,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | 361,000,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Included in Consolidated Statement of Income | (3,400,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | (7,900,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Included in Other Comprehensive Income | 5,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | (7,800,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Purchases | 201,400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | 145,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Settlements | (126,400,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | (123,200,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Sales | (79,000,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | (100,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Transfers Into Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | 5,800,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Transfers out of Level 3 | (1,200,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | (8,800,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Balance at End of Year | 360,600,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember | 364,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateDebtSecuritiesMember
Redeemable Preferred Stocks [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Balance at Beginning of Year | 7,400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | 4,700,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Included in Consolidated Statement of Income | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | 200,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Included in Other Comprehensive Income | (100,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | (1,300,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Purchases | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | 5,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Settlements | (600,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | (1,300,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Sales | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Transfers Into Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Transfers out of Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Balance at End of Year | 6,700,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember | 7,400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_MandatorilyRedeemablePreferredStockMember
Collateralized Loan Obligations [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Balance at Beginning of Year | 44,700,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Included in Consolidated Statement of Income | 200,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 200,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Included in Other Comprehensive Income | (1,000,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Purchases | 26,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 44,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Settlements | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Sales | (5,600,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Transfers Into Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Transfers out of Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Balance at End of Year | 64,400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember | 44,700,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_CollateralizedLoanObligationsMember
Other Mortgage and Asset-backed Securities [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Balance at Beginning of Year | 4,500,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | 100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Included in Consolidated Statement of Income | 100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | 100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Included in Other Comprehensive Income | 100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | (500,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Purchases | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | 4,500,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Settlements | (800,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | (100,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Sales | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | (2,000,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Transfers Into Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | 2,400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Transfers out of Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Balance at End of Year | 3,900,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember | 4,500,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_OtherMortgageandAssetbackedSecuritiesMember
Preferred and Common Stock [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Balance at Beginning of Year | 32,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | 13,300,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Included in Consolidated Statement of Income | 1,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | (1,000,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Included in Other Comprehensive Income | 500,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | 4,600,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Purchases | 8,900,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | 15,900,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Settlements | (4,500,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Sales | (2,200,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | (700,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Transfers Into Level 3 | 3,600,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Transfers out of Level 3 | (700,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Balance at End of Year | 38,800,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember | 32,100,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesInvestmentSummaryMember
Other Equity Interests [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Balance at Beginning of Year | 173,900,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | 141,300,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Included in Consolidated Statement of Income | 2,700,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | (1,600,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Included in Other Comprehensive Income | 2,200,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | 5,600,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Purchases | 53,000,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | 55,400,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Settlements | (39,800,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | (26,800,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Sales | (5,800,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Transfers Into Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Transfers out of Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Balance at End of Year | 186,200,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember | 173,900,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_OtherEquityInterestsMember
Fair Value Option Investments [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |
Balance at Beginning of Year | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |
Included in Consolidated Statement of Income | (700,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1 / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |
Included in Other Comprehensive Income | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |
Purchases | 58,000,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |
Settlements | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |
Sales | (4,000,000)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |
Transfers Into Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |
Transfers out of Level 3 | 0 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |
Balance at End of Year | $ 53,300,000 us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue / us-gaap_FairValueByAssetClassAxis = kmpr_FairValueOptionInvestmentsMember |

X
- Definition The amount of transfers of assets, liabilities, and financial instruments classified in shareholders' equity measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2. + References No definition available. + Details
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- Definition The amount of transfers of assets, liabilities, and financial instruments classified in shareholders' equity measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1. + References No definition available. + Details
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- Definition Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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