Policyholder Contract Liabilities - Policyholder Contract Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Policyholder Obligations	$ 700.6	$ 701.3
United Insurance Company of America \| Federal Home Loan Bank of Chicago
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
FHLB of Chicago Common Stock Owned at Cost	17.5	17.5
FHLB Funding Agreements \| United Insurance Company of America \| Federal Home Loan Bank of Chicago
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Policyholder Obligations	601.0	601.0
Universal Life-type Policyholder Account Balances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Policyholder Obligations	$ 99.6	$ 100.3

Carrying value as of the balance sheet date of the sum of the obligations to contract holders to provide to them an agreed upon rate of return pursuant to the terms of the underlying contract. These contracts represent lending by the contract holders to the entity in return for a guaranteed (primarily fixed) interest rate until maturity, unless called earlier if the contracts provide that option to the contract holders (usually institutions). There is little or no insurance risk for the entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.14)
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=123599499&loc=d3e63345-112809

+ Details

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

- Details

Name:	dei_LegalEntityAxis=kmpr_UnitedInsuranceCompanyOfAmericaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=srt_FederalHomeLoanBankOfChicagoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_FederalHomeLoanBankCertificatesAndObligationsFHLBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_OtherInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: