Investments - Distribution of Fixed Maturity Securities by Expected Maturity (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Percent of Total Fair Value
Due in 1 year or less	4.00%	4.00%
Due after 1 year through 5 years	26.20%	27.00%
Due after 5 years through 10 years	28.00%	27.70%
Due after 10 years through 20 years	25.10%	23.90%
Due after 20 years	16.70%	17.40%
Total	100.00%	100.00%
Fair Value
Due in 1 year or less	$ 227.5
Due after 1 year through 5 years	1,490.6
Due after 5 years through 10 years	1,591.0
Due after 10 years through 20 years	1,426.7
Due after 20 years	952.2
Total	5,688.0	$ 6,239.3
Amortized Cost, net
Due in 1 year or less	225.0
Due after 1 year through 5 years	1,527.0
Due after 5 years through 10 years	1,656.3
Due after 10 years through 20 years	1,534.6
Due after 10 years through 20 years, Amortized Cost	1,103.6
Amortized Cost, net	$ 6,046.5	$ 5,797.7
Average option-adjusted duration, in years	6 years 6 months	6 years 8 months 12 days