v3.26.3
Reserve for Unpaid Losses and Loss Adjustment Expenses - P&C Liabilities for Unpaid Losses and Loss Adjustment Expense (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Sep. 23, 2026
Dec. 31, 2025
Dec. 31, 2024
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]              
Beginning liabilities for unpaid losses and loss adjustment expenses, gross     $ 46,268        
Less: payments              
Ending liabilities for unpaid losses and loss adjustment expenses, gross $ 47,714   47,714        
Reinsurance Contract [Axis]: Adverse Development Cover A&E              
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]              
Reinsurance and other recoverables         $ 1,437    
Provision for unpaid losses and loss adjustment expense              
Change in deferred gain on retroactive reinsurance     (533)        
Increase (Decrease) in Deferred Revenue     36        
Less: payments              
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments         (1,437)    
Gain (Loss) on Contract Termination 497   497        
Reinsurance Contract [Axis]: Adverse Development Cover Navigators Group              
Provision for unpaid losses and loss adjustment expense              
Increase (Decrease) in Deferred Revenue   $ (8)   $ (64)      
Effect of Commutation Agreement [Member] | Reinsurance Contract [Axis]: Adverse Development Cover A&E              
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]              
Reinsurance and other recoverables         1,120    
Provision for unpaid losses and loss adjustment expense              
Increase (Decrease) in Deferred Revenue 317            
Less: payments              
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments         $ (1,120)    
Property, Liability and Casualty Insurance Product Line              
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]              
Beginning liabilities for unpaid losses and loss adjustment expenses, gross     38,155 36,404      
Reinsurance and other recoverables 5,187 6,627 5,187 6,627   $ 6,723 $ 6,753
Liability for Unpaid Claims and Claims Adjustment Expense, Net 34,262 31,112 34,262 31,112   31,432 29,651
Provision for unpaid losses and loss adjustment expense              
Current accident year     8,717 8,401      
Prior accident year development [1]     (746) (412)      
Total provision for unpaid losses and loss adjustment expenses     7,971 7,989      
Less: payments              
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year     (1,973) (2,038)      
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years     (4,993) (4,586)      
Total payments     (6,966) (6,624)      
Foreign currency adjustment     (6) 32      
Ending liabilities for unpaid losses and loss adjustment expenses, net 34,262 31,112 34,262 31,112      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments (5,187) (6,627) (5,187) (6,627)   $ (6,723) $ (6,753)
Ending liabilities for unpaid losses and loss adjustment expenses, gross $ 39,449 $ 37,739 39,449 37,739      
Property, Liability and Casualty Insurance Product Line | Reinsurance Contract [Axis]: Adverse Development Cover A&E              
Provision for unpaid losses and loss adjustment expense              
Change in deferred gain on retroactive reinsurance     (533)        
Property, Liability and Casualty Insurance Product Line | Reinsurance Contract [Axis]: Adverse Development Cover Navigators Group              
Provision for unpaid losses and loss adjustment expense              
Increase (Decrease) in Deferred Revenue       (64)      
Property, Liability and Casualty Insurance Product Line | Effect of Commutation Agreement [Member] | Reinsurance Contract [Axis]: Adverse Development Cover A&E              
Provision for unpaid losses and loss adjustment expense              
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)     $ 1,298 $ 0