v3.25.4
Reinsurance Contract Assets Held - Contracts measured under PAA (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Jan. 01, 2025
Dec. 31, 2024
Jan. 01, 2024
Reinsurance Contract Assets Held        
Reinsurance contract assets held $ 11,251.0   $ 10,682.6  
ARC        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 304.8   15.8  
AIC        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 10,946.2   10,666.8  
PAA        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 10,337.7 $ 9,757.2 9,757.2 $ 9,856.3
PAA | Property and Casualty Insurance and Reinsurance        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 10,330.5 9,748.3 9,748.3 9,853.7
PAA | Property and Casualty Insurance and Reinsurance | North American Insurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 1,354.3 1,149.2 1,149.2 1,180.3
PAA | Property and Casualty Insurance and Reinsurance | Global Insurers and Reinsurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 6,972.2 6,748.5 6,748.5 6,960.6
PAA | Property and Casualty Insurance and Reinsurance | International Insurers and Reinsurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 2,004.0 1,850.6 1,850.6 1,712.8
PAA | Life insurance and Run-off        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 7.2 8.9 8.9 2.6
PAA | ARC | Property and Casualty Insurance and Reinsurance | North American Insurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held (55.4) (87.0) (87.0) (70.0)
PAA | ARC | Property and Casualty Insurance and Reinsurance | Global Insurers and Reinsurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 91.7 (1.7) (1.7) (46.6)
PAA | ARC | Property and Casualty Insurance and Reinsurance | International Insurers and Reinsurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held (280.5) (460.0) (460.0) 296.7
PAA | AIC | Property and Casualty Insurance and Reinsurance | North American Insurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 1,409.7 1,236.2 1,236.2 1,250.3
PAA | AIC | Property and Casualty Insurance and Reinsurance | Global Insurers and Reinsurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held 6,880.5 6,750.2 6,750.2 7,007.2
PAA | AIC | Property and Casualty Insurance and Reinsurance | International Insurers and Reinsurers        
Reinsurance Contract Assets Held        
Reinsurance contract assets held $ 2,284.5 $ 2,310.6 $ 2,310.6 $ 1,416.1