Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479130/326-30-45-1

+ Details

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

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-4

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-14

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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Namespace Prefix:
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- Details

Name:	us-gaap_DebtInstrumentAxis=kmpr_SeniorNotes4.35PercentDueFebruary152025Member
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- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=kmpr_SeniorNotes3800PercentDueFebruary232032Member
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Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kmpr_SeniorNotes5875PercentDueMarch152062Member
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- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
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Schedule 2 - Parent Company Financial Statements - Balance Sheets (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Mar. 10, 2022	Feb. 15, 2022	Sep. 22, 2020
Amortized cost of fixed maturities	$ 7,565.8	$ 7,811.8
Long-term Debt	$ 1,213.4	1,195.1
Senior Notes \| Senior Notes, 4.35 Percent Due February 15, 2025
Stated interest rate, percentage	4.35%
Long-term debt, gross	$ 450.0
Senior Notes \| Senior Notes, 2.400 Percent Due September 30, 2030
Stated interest rate, percentage					2.40%
Long-term debt, gross	400.0
Proceeds from debt, net of issuance costs	395.8
Senior Notes \| Senior Notes, 3.800 Percent Due February 23, 2032
Stated interest rate, percentage				3.80%
Long-term debt, gross	400.0
Junior Debt \| Senior Notes, 5.875 Percent Due March 15, 2062
Stated interest rate, percentage			5.875%
Parent Company
Amortized cost of fixed maturities	177.4	122.5
Parent Company \| Senior Notes \| Senior Notes, 4.35 Percent Due February 15, 2025
Long-term Debt	$ 440.8	438.5
Stated interest rate, percentage	4.35%
Parent Company \| Senior Notes \| Senior Notes, 2.400 Percent Due September 30, 2030
Long-term Debt	$ 313.6	310.3
Stated interest rate, percentage	2.40%
Parent Company \| Senior Notes \| Senior Notes, 3.800 Percent Due February 23, 2032
Long-term Debt	$ 338.4	336.2
Stated interest rate, percentage	3.80%
Parent Company \| Junior Debt \| Senior Notes, 5.875 Percent Due March 15, 2062
Long-term Debt	$ 120.6	$ 110.1
Stated interest rate, percentage	5.875%