Investments - Distribution of Fixed Maturity Securities by Expected Maturity (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Percent of Total Fair Value
Due in 1 year Or less (percent)	3.90%	4.00%
Due after 1 year through 5 years (percent)	26.00%	27.00%
Due after 5 years through 10 years (percent)	28.30%	27.70%
Due after 10 years through 20 years (percent)	25.50%	23.90%
Due after 20 years (percent)	16.30%	17.40%
Total (percent)	100.00%	100.00%
Fair Value
Due in 1 year or less	$ 204.0
Due after 1 year through 5 years	1,369.3
Due after 5 years through 10 years	1,492.6
Due after 10 years through 20 years	1,348.3
Due after 20 years	857.9
Total	5,272.1	$ 6,239.3
Amortized Cost, net
Due in 1 year or less	204.6
Due after 1 year through 5 years	1,439.0
Due after 5 years through 10 years	1,621.7
Due after 10 years through 20 years	1,551.8
Due after 20 years	1,087.0
Amortized Cost, net	$ 5,904.1	$ 5,797.7
Average option-adjusted duration, in years	6 years 6 months	6 years 8 months 12 days