v3.26.1
Pension Plans, Retirement Benefits and Savings Plans (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Pension Plans [Member]    
Defined benefit plan disclosure    
Service cost $ 30 $ 28
Interest cost on benefit obligation 42 44
Expected return on plan assets (74) (70)
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit 0 0
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss 1 4
Total non-service cost (benefit) (31) (22)
Net periodic benefit cost (benefit) (1) 6
Pension Plans [Member] | Claims and claim adjustment expenses [Member]    
Defined benefit plan disclosure    
Service cost 11 11
Total non-service cost (benefit) (12) (8)
Pension Plans [Member] | General and administrative expenses [Member]    
Defined benefit plan disclosure    
Service cost 19 17
Total non-service cost (benefit) (19) (14)
Postretirement Benefit Plans [Member]    
Defined benefit plan disclosure    
Service cost 0 0
Interest cost on benefit obligation 1 1
Expected return on plan assets 0 0
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit 0 (1)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss (3) (3)
Total non-service cost (benefit) (2) (3)
Net periodic benefit cost (benefit) (2) (3)
Postretirement Benefit Plans [Member] | Claims and claim adjustment expenses [Member]    
Defined benefit plan disclosure    
Service cost 0 0
Total non-service cost (benefit) (1) (1)
Postretirement Benefit Plans [Member] | General and administrative expenses [Member]    
Defined benefit plan disclosure    
Service cost 0 0
Total non-service cost (benefit) $ (1) $ (2)