Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	$ 336.3
Capitalizations	122.2	$ 107.0	$ 94.4
Amortization expense	(111.1)	(101.2)	(88.2)	[1]
Balance, end of period	347.2	336.3
Whole Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	22.3	20.9	19.1
Capitalizations	3.0	2.7	3.0
Amortization expense	(1.3)	(1.2)	(1.2)
Experience adjustment	(0.2)	(0.1)	0.0
Balance, end of period	23.8	22.3	20.9
Term Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	32.6	30.0	27.5
Capitalizations	5.1	5.8	5.0
Amortization expense	(3.5)	(3.1)	(2.5)
Experience adjustment	0.0	(0.1)	0.0
Balance, end of period	34.2	32.6	30.0
Experience Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	5.7	5.8	6.0
Capitalizations	0.2	0.3	0.2
Amortization expense	(0.4)	(0.4)	(0.4)
Experience adjustment	0.0	0.0	0.0
Balance, end of period	5.5	5.7	5.8
Limited-Pay Whole Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	7.4	6.7	5.6
Capitalizations	1.1	1.1	1.4
Amortization expense	(0.4)	(0.3)	(0.3)
Experience adjustment	(0.1)	(0.1)	0.0
Balance, end of period	8.0	7.4	6.7
Indexed Universal Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	16.8	15.4	13.7
Capitalizations	3.6	2.5	2.5
Amortization expense	(1.1)	(1.0)	(0.8)
Experience adjustment	(0.1)	(0.1)	0.0
Balance, end of period	19.2	16.8	15.4
Supplemental Health
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	8.2	6.2	4.9
Capitalizations	3.4	2.9	1.8
Amortization expense	(0.8)	(0.6)	(0.5)
Experience adjustment	(0.2)	(0.3)	0.0
Balance, end of period	10.6	8.2	6.2
Total Annuities
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	214.0	221.1	223.3
Capitalizations	15.8	15.0	15.5
Amortization expense	(16.2)	(14.7)	(15.8)
Experience adjustment	(2.2)	(7.4)	(1.9)
Balance, end of period	$ 211.4	$ 214.0	$ 221.1

[1] Recast for the adoption of ASU 2018-12.