Basis of Presentation and Significant Accounting Policies - Schedule of Changes in DAC due to Adoption of ASU 2018-12 (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	$ 336.3	$ 330.6	[1]
Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	22.3	20.9		$ 19.1	$ 17.8
Term Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	32.6	30.0		27.5	25.6
Experience life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	5.7	5.8		6.0	6.2
Limited-pay whole life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	7.4	6.7		5.6	4.4
Indexed Universal Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	16.8	15.4		13.7	12.9
Supplemental health
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	8.2	6.2		4.9	4.3
Total Annuities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs	$ 214.0	221.1		$ 223.3	223.1
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		433.1
Previously Reported | Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					17.8
Previously Reported | Term Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					25.6
Previously Reported | Experience life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					2.6
Previously Reported | Limited-pay whole life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					4.4
Previously Reported | Indexed Universal Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					11.3
Previously Reported | Supplemental health
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					4.3
Previously Reported | Total Annuities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					137.7
Effect of the Adoption of ASU 2018-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		$ (102.5)
Effect of the Adoption of ASU 2018-12 | Whole Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					0.0
Effect of the Adoption of ASU 2018-12 | Term Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					0.0
Effect of the Adoption of ASU 2018-12 | Experience life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					3.6
Effect of the Adoption of ASU 2018-12 | Limited-pay whole life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					0.0
Effect of the Adoption of ASU 2018-12 | Indexed Universal Life
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					1.6
Effect of the Adoption of ASU 2018-12 | Supplemental health
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					0.0
Effect of the Adoption of ASU 2018-12 | Total Annuities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs					$ 85.4

[1] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements