Statutory Financial Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Traditional U.S. Life Insurance Subsidiaries
Statutory Accounting Practices
Statutory Net Income (Loss)	$ 1,329.9	$ 965.4	$ 779.5
Statutory Combined Net Gain (Loss) from Operations	1,351.5	965.4	681.1
Statutory Combined Capital and Surplus	3,751.3	3,816.3
Captive Reinsurers
Statutory Accounting Practices
Statutory Net Income (Loss)	(318.3)	(432.2)	(159.0)
Statutory Combined Net Gain (Loss) from Operations	(279.4)	(428.6)	$ (247.4)
Statutory Combined Capital and Surplus	$ 1,534.9	$ 1,229.6

Statutory Accounting Practices Statutory Net Gain (Loss) from Operations

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- 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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

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- Definition

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479989/944-505-50-1

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- Definition

Amount of net income for the period determined using accounting principles prescribed or permitted by insurance regulators.

+ References

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