Segment Information - Additional Significant Financial Information by Segment (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Segment Reporting Information [Line Items]
Assets	$ 14,965.9	$ 15,266.6
Corporate & Other
Segment Reporting Information [Line Items]
Assets	231.1	308.8
Operating Segments | Property & Casualty
Segment Reporting Information [Line Items]
Assets	1,402.5	1,372.1
Operating Segments | Life & Retirement
Segment Reporting Information [Line Items]
Assets	12,042.1	12,204.5
Operating Segments | Supplemental & Group Benefits
Segment Reporting Information [Line Items]
Assets	1,342.2	1,401.7
Intersegment eliminations
Segment Reporting Information [Line Items]
Assets	$ (52.0)	$ (20.5)