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Reserve for Unpaid Losses and Loss Adjustment Expenses - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2017
Dec. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]          
Unpaid losses and loss adjustment expenses $ 44,610 $ 42,318      
Asbestos and Environmental          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Change in Deferred Gain on Retroactive Reinsurance 62 194 $ 229    
Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Change in Deferred Gain on Retroactive Reinsurance 145 0 0    
Reinsurance Policy, Type [Axis]: Asbestos and Environmental | Asbestos and Environmental          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Reinsurance, Amount Retained, Per Policy       $ 1,700  
Retention Layer for Reserve for the Covered Liabilities as of the Inception Date [Member] | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Reinsurance, Amount Retained, Per Policy 1,816        
Retention Layer Above Reserve for the Covered Liabilities as of the Inception Date [Member] | Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Reinsurance, Amount Retained, Per Policy 100        
Group Benefits          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Prior accident year development [1] (561) (502) (381)    
Unpaid losses and loss adjustment expenses 8,206 8,274 8,160   $ 8,210
Group Benefits | Group long-term disability          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Unpaid losses and loss adjustment expenses 6,864        
Group Benefits | Disability Insurance Policy [Member]          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Prior accident year development [1] 483 457 325    
Group Benefits | Group life and accident, excluding premium waiver          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Prior accident year development [1] 80 36 50    
Unpaid losses and loss adjustment expenses 686        
Group Benefits | Group supplemental health          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Prior accident year development [1]   $ 9 $ 6    
Unpaid losses and loss adjustment expenses $ 39