Short-Duration Insurance Contracts - Schedule of Net Incurred and Paid Claims (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Short-Duration Insurance Contracts, Historical Claims Duration [Line Items]
Unpaid claims and claim expenses	$ 577.1	$ 569.2
Total short-duration insurance contracts
Short-Duration Insurance Contracts, Historical Claims Duration [Line Items]
Unpaid claims and claim expenses	525.7	525.5
Property & Casualty
Short-Duration Insurance Contracts, Historical Claims Duration [Line Items]
Unpaid claims and claim expenses	416.7	420.6
Group Benefits
Short-Duration Insurance Contracts, Historical Claims Duration [Line Items]
Unpaid claims and claim expenses	109.0	104.9	$ 114.3	$ 116.6
Other than short-duration
Short-Duration Insurance Contracts, Historical Claims Duration [Line Items]
Unpaid claims and claim expenses	$ 51.4	$ 43.7