Postretirement Benefits Other Than Pensions - Benefit Payments Net of Expected Medicare Part D Subsidy (Details) - Other Postretirement Benefit Plan, Defined Benefit $ in Millions	Dec. 31, 2019 USD ($)
Estimated Benefit Payments Excluding Medicare Part D Subsidy
2020	$ 1.3
2021	1.3
2022	1.3
2023	1.2
2024	1.2
2025-2029	4.5
Expected Medicare Part D Subsidy
2020	0.0
2021	0.0
2022	0.0
2023	0.0
2024	0.0
2025-2029	0.0
Net Estimated Benefit Payments
2020	1.3
2021	1.3
2022	1.3
2023	1.2
2024	1.2
2025-2029	$ 4.5

Defined Benefit Plan, Expected Future Benefit Payments Excluding Prescription Drug Subsidy Receipts, Next Twelve Months

No definition available.

Name:	kmpr_DefinedBenefitPlanExpectedFutureBenefitPaymentsExcludingPrescriptionDrugSubsidyReceiptsNextTwelveMonths
Namespace Prefix:	kmpr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Defined Benefit Plan, Expected Future Benefit Payments Excluding Prescription Drug Subsidy Receipts, Year Five

+ References

No definition available.

+ Details

Name:	kmpr_DefinedBenefitPlanExpectedFutureBenefitPaymentsExcludingPrescriptionDrugSubsidyReceiptsYearFive
Namespace Prefix:	kmpr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Defined Benefit Plan, Expected Future Benefit Payments Excluding Prescription Drug Subsidy Receipts, Year Four

+ References

No definition available.

+ Details

Name:	kmpr_DefinedBenefitPlanExpectedFutureBenefitPaymentsExcludingPrescriptionDrugSubsidyReceiptsYearFour
Namespace Prefix:	kmpr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Defined Benefit Plan, Expected Future Benefit Payments Excluding Prescription Drug Subsidy Receipts, Year Three

+ References

No definition available.

+ Details

Name:	kmpr_DefinedBenefitPlanExpectedFutureBenefitPaymentsExcludingPrescriptionDrugSubsidyReceiptsYearThree
Namespace Prefix:	kmpr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Defined Benefit Plan, Expected Future Benefit Payments Excluding Prescription Drug Subsidy Receipts, Year Two

+ References

No definition available.

+ Details

Name:	kmpr_DefinedBenefitPlanExpectedFutureBenefitPaymentsExcludingPrescriptionDrugSubsidyReceiptsYearTwo
Namespace Prefix:	kmpr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Defined Benefit Plan, Expected Future Benefit Payments Excluding Prescription Drug Subsidy Receipts, after Year Five

+ References

No definition available.

+ Details

Name:	kmpr_DefinedBenefitPlanExpectedFutureBenefitPaymentsExcludingPrescriptionDrugSubsidyReceiptsafterYearFive
Namespace Prefix:	kmpr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanEstimatedFutureBenefitPaymentsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits for defined benefit plan expected to be paid in fifth fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_DisclosureOfExpectedGrossPrescriptionDrugSubsidyReceiptsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_PostretirementMedicalPlansWithPrescriptionDrugBenefitsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of prescription drug subsidy receipts expected after fifth fiscal year following latest fiscal year.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

+ Details

Name:	us-gaap_PrescriptionDrugSubsidyReceiptsAfterYearFive
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of prescription drug subsidy receipts expected in next fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_PrescriptionDrugSubsidyReceiptsNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of prescription drug subsidy receipts expected in fifth fiscal year following latest fiscal year.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964

+ Details

Name:	us-gaap_PrescriptionDrugSubsidyReceiptsYearFive1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of prescription drug subsidy receipts expected in fourth fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_PrescriptionDrugSubsidyReceiptsYearFour1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of prescription drug subsidy receipts expected in third fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_PrescriptionDrugSubsidyReceiptsYearThree1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of prescription drug subsidy receipts expected in second fiscal year following latest fiscal year.

+ References

+ Details

Name:	us-gaap_PrescriptionDrugSubsidyReceiptsYearTwo1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: