v3.25.3
Pension Plans, Retirement Benefits and Savings Plans (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Pension Plans [Member]        
Defined benefit plan disclosure        
Service cost $ 28 $ 29 $ 85 $ 87
Interest cost on benefit obligation 44 43 132 129
Expected return on plan assets (71) (74) (211) (223)
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit 0 0 0 0
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss 4 2 11 5
Total non-service cost (benefit) (23) (29) (68) (89)
Net periodic benefit cost (benefit) 5 0 17 (2)
Pension Plans [Member] | Claims and claim adjustment expenses [Member]        
Defined benefit plan disclosure        
Service cost 11 11 33 34
Total non-service cost (benefit) (9) (11) (26) (34)
Pension Plans [Member] | General and administrative expenses [Member]        
Defined benefit plan disclosure        
Service cost 17 18 52 53
Total non-service cost (benefit) (14) (18) (42) (55)
Postretirement Benefit Plans [Member]        
Defined benefit plan disclosure        
Service cost 0 0 0 0
Interest cost on benefit obligation 1 1 2 3
Expected return on plan assets 0 0 0 0
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit 0 0 (1) (2)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss (3) (3) (9) (7)
Total non-service cost (benefit) (2) (2) (8) (6)
Net periodic benefit cost (benefit) (2) (2) (8) (6)
Postretirement Benefit Plans [Member] | Claims and claim adjustment expenses [Member]        
Defined benefit plan disclosure        
Service cost 0 0 0 0
Total non-service cost (benefit) (1) 0 (3) (2)
Postretirement Benefit Plans [Member] | General and administrative expenses [Member]        
Defined benefit plan disclosure        
Service cost 0 0 0 0
Total non-service cost (benefit) $ (1) $ (2) $ (5) $ (4)