v3.26.3
Insurance Claim Reserves (Details) - Prior Year Reserve Development - Property-casualty [Member] - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Liability for claims and claim adjustment expense        
Net favorable development included in estimated claims and claim adjustment expenses incurred for claims arising in prior years     $ 1,148 $ 648
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations     1,230 715
Accretion expense     32 32
Business Insurance [Member]        
Liability for claims and claim adjustment expense        
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations $ 41 $ (125) 522 28
Business Insurance [Member] | Asbestos reserves [Member]        
Liability for claims and claim adjustment expense        
Increase to reserves 295 277 295 277
Bond & Specialty Insurance [Member]        
Liability for claims and claim adjustment expense        
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations 95 43 235 191
Personal Insurance [Member]        
Liability for claims and claim adjustment expense        
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations $ 98 $ 104 $ 468 $ 496