Fair Value of Financial Instruments - Financial Instrument Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Level 1
Investments
Other investments	$ 0.0	$ 0.0
Deposit asset on reinsurance	0.0	0.0
Financial Liabilities
Investment contract and future policy benefit reserves, fixed annuity contracts	0.0	0.0
Investment contract and future policy benefit reserves, account values on life contracts	0.0	0.0
Other policyholder funds	0.0	0.0
Reverse repurchase agreements	0.0	0.0
Short-term debt	0.0	0.0
Long-term debt	0.0	0.0
Level 2
Investments
Other investments	0.0	0.0
Deposit asset on reinsurance	0.0	0.0
Financial Liabilities
Investment contract and future policy benefit reserves, fixed annuity contracts	0.0	0.0
Investment contract and future policy benefit reserves, account values on life contracts	0.0	0.0
Other policyholder funds	904.9	810.7
Reverse repurchase agreements	0.4	73.3
Short-term debt	0.0	0.0
Long-term debt	541.1	240.5
Level 3
Investments
Other investments	185.0	170.9
Deposit asset on reinsurance	2,070.3	2,207.2
Financial Liabilities
Investment contract and future policy benefit reserves, fixed annuity contracts	4,821.1	4,901.3
Investment contract and future policy benefit reserves, account values on life contracts	112.8	107.7
Other policyholder funds	11.0	52.3
Reverse repurchase agreements	0.0	0.0
Short-term debt	0.0	249.0
Long-term debt	0.0	0.0
Carrying Amount
Investments
Other investments	181.6	167.4
Deposit asset on reinsurance	2,515.7	2,516.6
Financial Liabilities
Investment contract and future policy benefit reserves, fixed annuity contracts	4,920.8	4,988.5
Investment contract and future policy benefit reserves, account values on life contracts	116.8	111.9
Other policyholder funds	915.9	863.0
Reverse repurchase agreements	0.2	70.2
Short-term debt	0.0	249.0
Long-term debt	546.1	249.0
Fair Value
Investments
Other investments	185.0	170.9
Deposit asset on reinsurance	2,070.3	2,207.2
Financial Liabilities
Investment contract and future policy benefit reserves, fixed annuity contracts	4,821.1	4,901.3
Investment contract and future policy benefit reserves, account values on life contracts	112.8	107.7
Other policyholder funds	915.9	863.0
Reverse repurchase agreements	0.4	73.3
Short-term debt	0.0	249.0
Long-term debt	$ 541.1	$ 240.5

Deposit Asset On Reinsurance Fair Value Disclosure

No definition available.

Name:	hmn_DepositAssetOnReinsuranceFairValueDisclosure
Namespace Prefix:	hmn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The fair value of accrued obligation to policyholders that relates to insured events under individual and group annuities and supplementary insurance contracts.

+ References

No definition available.

+ Details

Name:	hmn_LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValue
Namespace Prefix:	hmn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Liability for policyholder account balances life fair value.

+ References

No definition available.

+ Details

Name:	hmn_LiabilityForPolicyHolderAccountBalancesLifeFairValue
Namespace Prefix:	hmn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair Value of the liability as of the balance sheet date to the policyholders for funds held that are returnable under the terms of insurance contracts that were not separately reported.

+ References

No definition available.

+ Details

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Namespace Prefix:	hmn_
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Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
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Period Type:	duration

- References

No definition available.

+ Details

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- 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

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

- Definition

Amount of investments classified as other.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_OtherInvestments
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying value of securities purchased to be resold in reverse repurchase transactions as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity 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. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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Period Type:	instant

- Details

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- Details

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- Details

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