Deposit Asset on Reinsurance - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Effects of Reinsurance [Line Items]
Reinsurance block of in-force fixed and variable annuity business	$ 3,100.0
Minimum crediting rating (percent)	4.50%
Percentage of forced fixed annuities (percent)	50.00%
Fixed annuity reserves reinsured on a coinsurance basis	$ 2,400.0
Net investment income	444.8	$ 400.9	[1]	$ 422.5	[1]
Separate account asset	3,294.1	2,792.3	[2]
Separate account liability	3,294.1	2,792.3	[2]
Reinsurance Contract Modified Coinsurance Basis
Effects of Reinsurance [Line Items]
Separate account asset	700.0
Separate account liability	700.0
Deposit Asset On Reinsurance
Effects of Reinsurance [Line Items]
Net investment income	$ 104.9	$ 103.5		$ 101.1

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

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