Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period			$ 336.3
Amortization expense	$ (28.1)	$ (26.3)	(82.1)	$ (75.4)
Balance, end of period	345.4		345.4
Whole Life Insurance
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	23.0		22.3
Capitalizations	0.8		2.2
Amortization expense	(0.4)		(1.0)
Experience adjustment	0.0		(0.1)
Balance, end of period	23.4		23.4
Term Life Insurance
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	33.5		32.6
Capitalizations	1.2		3.8
Amortization expense	(0.9)		(2.6)
Experience adjustment	0.0		0.0
Balance, end of period	33.8		33.8
Experience Life Insurance
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	5.6		5.7
Capitalizations	0.1		0.2
Amortization expense	(0.1)		(0.3)
Experience adjustment	0.0		0.0
Balance, end of period	5.6		5.6
Limited Pay Whole Life Insurance
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	7.7		7.4
Capitalizations	0.3		0.8
Amortization expense	(0.1)		(0.3)
Experience adjustment	(0.1)		(0.1)
Balance, end of period	7.8		7.8
Indexed Universal Life Insurance
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	17.8		16.8
Capitalizations	0.8		2.4
Amortization expense	(0.3)		(0.8)
Experience adjustment	0.0		(0.1)
Balance, end of period	18.3		18.3
Supplemental health
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	9.3		8.2
Capitalizations	0.8		2.4
Amortization expense	(0.2)		(0.6)
Experience adjustment	0.0		(0.1)
Balance, end of period	9.9		9.9
Total Annuities
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	212.4		214.0
Capitalizations	3.9		11.9
Amortization expense	(4.1)		(12.0)
Experience adjustment	(0.2)		(1.9)
Balance, end of period	$ 212.0		$ 212.0