Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	$ 347.2
Capitalizations	31.4	$ 27.9
Amortization expense	(29.6)	(27.0)
Balance, end of period	349.2
Whole Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	23.8	22.3
Capitalizations	0.6	0.7
Amortization expense	(0.3)	(0.3)
Experience adjustment	0.0	(0.1)
Balance, end of period	24.1	22.6
Term Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	34.2	32.6
Capitalizations	1.2	1.2
Amortization expense	(0.9)	(0.9)
Experience adjustment	0.0	0.0
Balance, end of period	34.5	32.9
Experience life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	5.5	5.7
Capitalizations	0.0	0.1
Amortization expense	(0.1)	(0.1)
Experience adjustment	0.0	0.0
Balance, end of period	5.4	5.7
Limited-Pay Whole Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	8.0	7.4
Capitalizations	0.1	0.2
Amortization expense	(0.1)	(0.1)
Experience adjustment	0.0	0.0
Balance, end of period	8.0	7.5
Indexed Universal Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	19.2	16.8
Capitalizations	0.8	0.7
Amortization expense	(0.2)	(0.3)
Experience adjustment	0.0	(0.1)
Balance, end of period	19.8	17.1
Supplemental health
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	10.6	8.2
Capitalizations	1.0	0.8
Amortization expense	(0.3)	(0.2)
Experience adjustment	(0.1)	(0.1)
Balance, end of period	11.2	8.7
Total Annuities
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	211.4	214.0
Capitalizations	3.6	3.9
Amortization expense	(4.0)	(3.7)
Experience adjustment	(0.6)	(1.3)
Balance, end of period	$ 210.4	$ 212.9