v3.26.1
Claim and Claim Adjustment Expense Reserves (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Dec. 31, 2014
Dec. 31, 2010
Liability for Claims and Claims Adjustment Expense [Line Items]          
Largest recoverable from single reinsurer $ 6,387   $ 6,381    
Pretax (favorable) unfavorable premium development, excluding Life & Group 100 $ 83      
Reinsurance premiums paid 9 0      
Retroactive reinsurance benefit recognized 22 17      
Unusual or Infrequent Item, or Both, Net of Insurance Proceeds 88 97      
California Wildfires          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Unusual or Infrequent Item, or Both, Net of Insurance Proceeds   53      
Corporate & Other          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Pretax (favorable) unfavorable premium development, excluding Life & Group 0 $ 22      
Asbestos and Environmental Reserves          
Liability for Claims and Claims Adjustment Expense [Line Items]          
Net A&EP claim and allocated claim adjustment expense reserves ceded to NICO         $ 1,600
Aggregate limit under A&EP Loss Portfolio Transfer         4,000
A&EP claim and allocated claim adjustment expense reserves ceded under existing third party reinsurance contracts transferred to NICO under A&EP Loss Portfolio Transfer         1,200
Reinsurance premium paid to NICO under A&EP Loss Portfolio Transfer         2,000
Net reinsurance receivables transferred to NICO under A&EP Loss Portfolio Transfer         215
Total consideration paid to NICO under AEP Loss Portfolio Transfer       $ 2,200 $ 2,200
Cumulative amounts ceded under AEP Loss Portfolio Transfer 3,900        
Deferred reinsurance benefit yet to be recognized 448   $ 470    
Fair value of collateral trust account established by NICO under A&EP Loss Portfolio Transfer $ 2,600