Long-Duration Insurance Contracts - Deferred Policy Acquisition Costs, Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period			$ 330.6
Amortization expense	$ (26.3)	$ (22.2)	(75.4)	$ (65.7)
Balance, end of period	334.9		334.9		$ 330.6
Previously Reported
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period			433.1
Amortization expense		(23.3)		(76.7)
Balance, end of period					433.1
Effect of the Adoption of ASU 2018-12
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period			(102.5)
Amortization expense		$ 1.1		11.0
Balance, end of period					(102.5)
Whole Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	21.6		20.9	19.1	19.1	$ 17.8
Capitalizations	0.7		2.0		3.0	2.4
Amortization expense	(0.3)		(0.9)		(1.2)	(1.1)
Experience adjustment	(0.1)		(0.1)		0.0	0.0
Balance, end of period	21.9		21.9		20.9	19.1
Whole Life | Previously Reported
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						17.8
Whole Life | Effect of the Adoption of ASU 2018-12
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						0.0
Term Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	31.4		30.0	27.5	27.5	25.6
Capitalizations	1.5		4.3		5.0	4.2
Amortization expense	(0.8)		(2.2)		(2.5)	(2.3)
Experience adjustment	(0.1)		(0.1)		0.0	0.0
Balance, end of period	32.0		32.0		30.0	27.5
Term Life | Previously Reported
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						25.6
Term Life | Effect of the Adoption of ASU 2018-12
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						0.0
Experience Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	5.7		5.8	6.0	6.0	6.2
Capitalizations	0.1		0.2		0.2	0.2
Amortization expense	(0.1)		(0.3)		(0.4)	(0.4)
Experience adjustment	0.0		0.0		0.0	0.0
Balance, end of period	5.7		5.7		5.8	6.0
Experience Life | Previously Reported
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						2.6
Experience Life | Effect of the Adoption of ASU 2018-12
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						3.6
Limited Pay Whole Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	7.0		6.7	5.6	5.6	4.4
Capitalizations	0.4		0.9		1.4	1.5
Amortization expense	(0.1)		(0.3)		(0.3)	(0.3)
Experience adjustment	(0.1)		(0.1)		0.0	0.0
Balance, end of period	7.2		7.2		6.7	5.6
Limited Pay Whole Life | Previously Reported
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						4.4
Limited Pay Whole Life | Effect of the Adoption of ASU 2018-12
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						0.0
Indexed Universal Life
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	16.1		15.4	13.7	13.7	12.9
Capitalizations	0.6		1.8		2.5	1.7
Amortization expense	(0.2)		(0.7)		(0.8)	(0.8)
Experience adjustment	(0.1)		(0.1)		0.0	(0.1)
Balance, end of period	16.4		16.4		15.4	13.7
Indexed Universal Life | Previously Reported
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						11.3
Indexed Universal Life | Effect of the Adoption of ASU 2018-12
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						1.6
Supplemental health
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	7.0		6.2	4.9	4.9	4.3
Capitalizations	0.7		2.0		1.8	1.1
Amortization expense	(0.2)		(0.5)		(0.5)	(0.5)
Experience adjustment	0.0		(0.2)		0.0	0.0
Balance, end of period	7.5		7.5		6.2	4.9
Supplemental health | Previously Reported
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						4.3
Supplemental health | Effect of the Adoption of ASU 2018-12
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						0.0
Total Annuities
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	217.2		221.1	$ 223.3	223.3	223.1
Capitalizations	3.7		11.4		15.5	17.3
Amortization expense	(3.6)		(11.0)		(15.8)	(16.0)
Experience adjustment	(2.3)		(6.5)		(1.9)	(1.1)
Balance, end of period	$ 215.0		$ 215.0		$ 221.1	223.3
Total Annuities | Previously Reported
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						137.7
Total Annuities | Effect of the Adoption of ASU 2018-12
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period						$ 85.4