Reinsurance - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Number of companies that make up majority of reinsurance recoverable	9
Prepaid Reinsurance Premiums	$ 508.0	$ 549.4
Reinsurance Recoverables	8,296.4	9,108.4
Closed Block Individual Disability Reinsurance Transaction
Deposit Contracts, Assets	282.3	296.5
Amortization of Prepaid Reinsurance Premium	41.4	44.1	$ 50.3
Prepaid Reinsurance Premiums	508.1	549.5
Reinsurance Recoverables	$ 4,698.4	$ 5,143.4
AM Best A Rating or Better \| Reinsurer Concentration Risk \| Reinsurance Recoverable \| Commonwealth Annuity and Life Insurance Company
Percentage of Concentration Risk	56.00%
AM Best A Rating or Better \| Reinsurer Concentration Risk \| Reinsurance Recoverable \| Top 9 Reinsurers
Percentage of Concentration Risk	39.00%
AM Best, A- Rating \| Reinsurer Concentration Risk \| Reinsurance Recoverable \| Other Reinsurers
Percentage of Concentration Risk	4.00%
AM Best, Below A- or Not Rated \| Reinsurer Concentration Risk \| Reinsurance Recoverable \| Other Reinsurers
Percentage of Concentration Risk	1.00%

Amortization of Prepaid Reinsurance Premium

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Number of companies that make up majority of reinsurance recoverable

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Carrying amount of assets as of the balance sheet date pertaining to amounts paid by the insured (including a ceding company) under insurance or reinsurance contracts for which insurance risk is not transferred.

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The unexpired portion of premiums ceded on policies in force as of the balance sheet date.

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Amount, after valuation allowance, recoverable under reinsurance contracts including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

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