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Investments - Distribution of Fixed Maturity Securities by Expected Maturity (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2023	Jun. 30, 2022	Dec. 31, 2022
Percent of Total Fair Value
Due in 1 year Or less (percent)	4.70%		4.40%
Due after 1 year through 5 years (percent)	26.00%		26.30%
Due after 5 years through 10 years (percent)	28.10%		27.90%
Due after 10 years through 20 years (percent)	25.00%		25.00%
Due after 20 years (percent)	16.20%		16.40%
Total (percent)	100.00%		100.00%
Fair Value
Due in 1 year or less	$ 249.5
Due after 1 year through 5 years	1,392.5
Due after 5 years through 10 years	1,501.0
Due after 10 years through 20 years	1,342.2
Due after 20 years	864.8
Total	5,350.0		$ 5,185.0
Amortized Cost, net
Due in 1 year or less	256.3
Due after 1 year through 5 years	1,441.9
Due after 5 years through 10 years	1,581.4
Due after 10 years through 20 years	1,482.3
Due after 20 years	1,041.4
Amortized Cost, net	$ 5,803.3		$ 5,756.9
Average option-adjusted duration, in years	6 years 3 months 18 days	6 years 4 months 24 days

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