v3.25.4
Financial Risk Management - Concentration of insurance risk (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Financial Risk Management.    
Insurance $ 31,595.0 $ 31,064.1
Reinsurance $ (5,522.1) (6,197.7)
Reserving risk    
Asbestos and environmental claims, maximum settlement period (in years) 40 years  
Catastrophe risk    
Normalized Net Earnings, Percent Return On Common Shareholders' Equity Adjusted To Pre-Tax Basis 15.00%  
Carrying amount of catastrophe claims liability $ 130,000.0  
Canada    
Financial Risk Management.    
Insurance 2,796.7 2,869.1
United States    
Financial Risk Management.    
Insurance 18,143.5 17,167.6
Middle East and Asia    
Financial Risk Management.    
Insurance 4,401.0 5,249.5
Other International    
Financial Risk Management.    
Insurance 6,253.8 5,777.9
Property    
Financial Risk Management.    
Insurance 11,130.5 10,796.9
Casualty    
Financial Risk Management.    
Insurance 17,277.3 16,820.5
Specialty    
Financial Risk Management.    
Insurance 3,187.2 3,446.7
Insurance risk    
Financial Risk Management.    
Insurance 31,595.0 31,064.1
Reinsurance (5,522.1) (6,197.7)
Net insurance revenue 26,072.9 24,866.4
Insurance risk | Canada    
Financial Risk Management.    
Insurance 2,796.6 2,868.9
Reinsurance (257.7) (265.9)
Net insurance revenue 2,538.9 2,603.0
Insurance risk | United States    
Financial Risk Management.    
Insurance 18,143.6 17,167.9
Reinsurance (2,855.7) (2,870.7)
Net insurance revenue 15,287.9 14,297.2
Insurance risk | Middle East and Asia    
Financial Risk Management.    
Insurance 4,401.1 5,249.6
Reinsurance (1,137.0) (1,790.5)
Net insurance revenue 3,264.1 3,459.1
Insurance risk | Other International    
Financial Risk Management.    
Insurance 6,253.7 5,777.7
Reinsurance (1,271.7) (1,270.6)
Net insurance revenue 4,982.0 4,507.1
Insurance risk | Property    
Financial Risk Management.    
Net insurance revenue 9,008.9 8,524.4
Insurance risk | Property | Canada    
Financial Risk Management.    
Net insurance revenue 1,397.3 1,392.4
Insurance risk | Property | United States    
Financial Risk Management.    
Net insurance revenue 4,071.0 3,828.1
Insurance risk | Property | Middle East and Asia    
Financial Risk Management.    
Net insurance revenue 1,338.7 1,320.3
Insurance risk | Property | Other International    
Financial Risk Management.    
Net insurance revenue 2,201.9 1,983.6
Insurance risk | Casualty    
Financial Risk Management.    
Net insurance revenue 14,574.4 13,739.6
Insurance risk | Casualty | Canada    
Financial Risk Management.    
Net insurance revenue 1,040.2 1,113.8
Insurance risk | Casualty | United States    
Financial Risk Management.    
Net insurance revenue 10,316.7 9,582.3
Insurance risk | Casualty | Middle East and Asia    
Financial Risk Management.    
Net insurance revenue 1,336.0 1,274.1
Insurance risk | Casualty | Other International    
Financial Risk Management.    
Net insurance revenue 1,881.5 1,769.4
Insurance risk | Specialty    
Financial Risk Management.    
Net insurance revenue 2,489.6 2,602.4
Insurance risk | Specialty | Canada    
Financial Risk Management.    
Net insurance revenue 101.4 96.8
Insurance risk | Specialty | United States    
Financial Risk Management.    
Net insurance revenue 900.2 886.8
Insurance risk | Specialty | Middle East and Asia    
Financial Risk Management.    
Net insurance revenue 589.4 864.7
Insurance risk | Specialty | Other International    
Financial Risk Management.    
Net insurance revenue 898.6 754.1
Life insurance and Run-off    
Financial Risk Management.    
Insurance 253.3 189.6
Life insurance and Run-off | United States    
Financial Risk Management.    
Insurance 36.7 10.9
Life insurance and Run-off | Middle East and Asia    
Financial Risk Management.    
Insurance 59.9 42.0
Life insurance and Run-off | Other International    
Financial Risk Management.    
Insurance 156.7 136.7
Life insurance and Run-off | Property    
Financial Risk Management.    
Insurance 1.3  
Life insurance and Run-off | Casualty    
Financial Risk Management.    
Insurance 35.4 10.9
Life insurance and Run-off | Specialty    
Financial Risk Management.    
Insurance 216.6 178.7
Life insurance and Run-off | Insurance risk    
Financial Risk Management.    
Net insurance revenue $ 181.5 $ 151.9