v3.25.4
Business Segments - Earned Premiums by Product Line (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums [1] $ 4,396.3 $ 4,215.9 $ 4,529.4
Life Insurance      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums (8.7) (7.2) (19.1)
Operating Segments      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums 4,319.1 3,970.3 4,020.1
Operating Segments | Specialty Property & Casualty Insurance      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums 3,925.7 3,576.4 3,632.5
Operating Segments | Specialty Property & Casualty Insurance | Personal Automobile      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums 3,024.9 2,851.4 2,977.8
Operating Segments | Specialty Property & Casualty Insurance | Commercial Automobile      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums 900.8 725.0 654.7
Operating Segments | Life Insurance      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums 393.4 393.9 387.6
Operating Segments | Life Insurance | Life      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums 330.6 328.1 319.2
Operating Segments | Life Insurance | Accident and Health      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums 21.8 22.3 23.1
Operating Segments | Life Insurance | Property      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums 41.0 43.5 45.3
Non-Core Operations      
Entity-Wide Information, Revenue from External Customer [Line Items]      
Earned Premiums $ 77.2 $ 245.6 $ 509.3
[1]
1 Includes a remeasurement loss related to the deferred profit liability within the Life Insurance business of $8.7 million for the year ended December 31, 2025, a remeasurement loss of $7.2 million for the year ended December 31, 2024, and a remeasurement loss of $19.1 million for the year ended December 31, 2023.