Investments - Maturities of Fixed Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Amortized Cost, net
Due in 1 year or less	$ 299.2
Due after 1 year through 5 years	1,291.2
Due after 5 years through 10 years	1,586.2
Due after 10 years through 20 years	1,682.8
Due after 20 years	1,167.3
Amortized Cost, net	6,026.7	$ 5,842.5
Fair Value
Due in 1 year or less	298.9
Due after 1 year through 5 years	1,278.9
Due after 5 years through 10 years	1,556.7
Due after 10 years through 20 years	1,556.9
Due after 20 years	1,023.2
Total	$ 5,714.6	$ 5,387.9
Percent of Total Fair Value
Due in 1 year or less	5.20%
Due after 1 year through 5 years	22.40%
Due after 5 years through 10 years	27.20%
Due after 10 years through 20 years	27.30%
Due after 20 years	17.90%
Total	100.00%