Investments - Distribution of Fixed Maturity Securities by Expected Maturity (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Percent of Total Fair Value
Due in 1 year or less	4.10%	4.00%
Due after 1 year through 5 years	27.40%	27.00%
Due after 5 years through 10 years	27.20%	27.70%
Due after 10 years through 20 years	24.10%	23.90%
Due after 20 years	17.20%	17.40%
Total	100.00%	100.00%
Fair Value
Due in 1 year or less	$ 248.0
Due after 1 year through 5 years	1,638.0
Due after 5 years through 10 years	1,626.1
Due after 10 years through 20 years	1,443.1
Due after 20 years	1,032.2
Fixed maturity securities, available for sale, at fair value (amortized cost, net 2022, $5,970.7; 2021, $5,797.7)	5,987.4	$ 6,239.3
Amortized Cost, net
Due in 1 year or less	248.0
Due after 1 year through 5 years	1,628.4
Due after 5 years through 10 years	1,599.9
Due after 10 years through 20 years	1,429.5
Due after 10 years through 20 years, Amortized Cost	1,064.9
Amortized Cost, net	$ 5,970.7	$ 5,797.7
Average option-adjusted duration, in years	6 years 7 months 6 days	6 years 8 months 12 days