Fair Value Measurements - Schedule of Financial Instruments Based on Observable Inputs (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025	Jun. 13, 2025	Oct. 20, 2020	Jul. 02, 2020
Fixed Rate Reset Subordinated Notes due 2055 \| Subordinated Debt
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Interest rate, stated percentage	7.75%	7.75%
Fixed Rate Reset Subordinated Notes due 2055 \| Junior Subordinated Debt
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Interest rate, stated percentage			7.75%
Senior Notes Due 2030 \| Senior Notes
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Interest rate, stated percentage	4.875%	4.875%			4.875%
Fixed Rate Reset Junior Subordinated notes due 2041 \| Junior Subordinated Debt
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Interest rate, stated percentage	6.625%	6.625%		6.625%
Fair Value \| 7.750% Subordinated notes due 2055 \| Subordinated Debt \| Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	$ 421.9	$ 431.0
Fair Value \| 4.875% Senior notes due 2030 \| Senior Notes \| Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	320.9	327.7
Fair Value \| 6.625% Fixed Rate Reset Junior Subordinated notes due 2041 \| Junior Subordinated Debt \| Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	0.0	124.4
Carrying Value \| 7.750% Subordinated notes due 2055 \| Subordinated Debt \| Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	393.7	393.5
Carrying Value \| 4.875% Senior notes due 2030 \| Senior Notes \| Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	326.8	326.4
Carrying Value \| 6.625% Fixed Rate Reset Junior Subordinated notes due 2041 \| Junior Subordinated Debt \| Level 2
Fair Value Disclosure, Asset and Liability, Not Measured at Fair Value [Line Items]
Debt instrument, fair value disclosure	$ 0.0	$ 123.3