v3.25.2
Pension Plans, Retirement Benefits and Savings Plans (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Pension Plans [Member]        
Defined benefit plan disclosure        
Service cost $ 29 $ 29 $ 57 $ 58
Interest cost on benefit obligation 44 43 88 86
Expected return on plan assets (70) (74) (140) (149)
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 3 1 7 3
Total non-service cost (benefit) (23) (30) (45) (60)
Net periodic benefit cost (benefit) 6 (1) 12 (2)
Pension Plans [Member] | Claims and claim adjustment expenses [Member]        
Defined benefit plan disclosure        
Service cost 11 12 22 23
Total non-service cost (benefit) (9) (11) (17) (23)
Pension Plans [Member] | General and administrative expenses [Member]        
Defined benefit plan disclosure        
Service cost 18 17 35 35
Total non-service cost (benefit) (14) (19) (28) (37)
Postretirement Benefit Plans [Member]        
Defined benefit plan disclosure        
Service cost 0 0 0 0
Interest cost on benefit obligation 0 1 1 2
Expected return on plan assets 0 0 0 0
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit 0 (1) (1) (2)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss (3) (2) (6) (4)
Total non-service cost (benefit) (3) (2) (6) (4)
Net periodic benefit cost (benefit) (3) (2) (6) (4)
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) (1) (2) (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) $ (2) $ (1) $ (4) $ (2)