Long-Duration Insurance Contracts - Separate Account Liability Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022
Separate Account, Liability [Roll Forward]
Balance, beginning of year	[1]	$ 2,792.3
Balance, end of period		3,294.1	$ 2,792.3	[1]
Variable Account Annuities
Separate Account, Liability [Roll Forward]
Balance, beginning of year		2,792.3	3,441.0
Deposits		234.2	240.3
Withdrawals		(213.4)	(186.8)
Net transfers		(15.5)	(38.1)
Fees and charges		(37.6)	(36.8)
Market appreciation (depreciation)		541.5	(619.7)
Other		(7.4)	(7.6)
Balance, end of period		$ 3,294.1	$ 2,792.3

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