Fair Value of Financial Instruments - Financial Instrument Not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Level 1
Investments
Other investments	$ 0.0	$ 0.0
Deposit asset on reinsurance	0.0	0.0
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	0.0	0.0
Investment contract and policy reserves, account values on life contracts	0.0	0.0
Other policyholder funds	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 policy reserves, fixed annuity contracts	0.0	0.0
Investment contract and policy reserves, account values on life contracts	0.0	0.0
Other policyholder funds	842.9	782.8
Short-term debt	0.0	0.0
Long-term debt	265.8	277.4
Level 3
Investments
Other investments	175.5	152.4
Deposit asset on reinsurance	2,628.4	2,935.1
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	5,021.8	5,004.9
Investment contract and policy reserves, account values on life contracts	116.9	115.4
Other policyholder funds	67.8	56.5
Short-term debt	249.0	249.0
Long-term debt	0.0	0.0
Carrying Amount
Investments
Other investments	172.0	148.8
Deposit asset on reinsurance	2,491.8	2,481.5
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	4,958.0	4,941.3
Investment contract and policy reserves, account values on life contracts	106.9	105.4
Other policyholder funds	910.7	839.3
Short-term debt	249.0	249.0
Long-term debt	253.7	253.6
Fair Value
Investments
Other investments	175.5	152.4
Deposit asset on reinsurance	2,628.4	2,935.1
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	5,021.8	5,004.9
Investment contract and policy reserves, account values on life contracts	116.9	115.4
Other policyholder funds	910.7	839.3
Short-term debt	249.0	249.0
Long-term debt	$ 265.8	$ 277.4

Deposit Asset On Reinsurance Fair Value Disclosure

No definition available.

Name:	hmn_DepositAssetOnReinsuranceFairValueDisclosure
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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
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Balance Type:	credit
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- Definition

Liability for policyholder account balances life fair value.

+ References

No definition available.

+ Details

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- 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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- References

No definition available.

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- References

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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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Period Type:	instant

- Definition

Amount of investments classified as other.

+ References

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 210.7-03.1(f,g))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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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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