Pension Plans, Retirement Benefits and Savings Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Pension Plans [Member]
Defined benefit plan disclosure
Service cost	$ 37	$ 36	$ 73	$ 71
Interest cost on benefit obligation	26	20	51	41
Expected return on plan assets	(74)	(68)	(148)	(137)
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	13	27	25	54
Total non-service cost (benefit)	(35)	(21)	(72)	(42)
Net periodic benefit cost (benefit)	2	15	1	29
Pension Plans [Member] | Claims and claim adjustment expenses [Member]
Defined benefit plan disclosure
Service cost	15	15	30	29
Total non-service cost (benefit)	(14)	(8)	(29)	(17)
Pension Plans [Member] | General and administrative expenses [Member]
Defined benefit plan disclosure
Service cost	22	21	43	42
Total non-service cost (benefit)	(21)	(13)	(43)	(25)
Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Service cost	0	0	0	0
Interest cost on benefit obligation	1	0	2	1
Expected return on plan assets	0	0	0	0
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit	(1)	(1)	(2)	(2)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss	(1)	0	(2)	(1)
Total non-service cost (benefit)	(1)	(1)	(2)	(2)
Net periodic benefit cost (benefit)	(1)	(1)	(2)	(2)
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)	(1)	(1)
Postretirement Benefit Plans [Member] | General and administrative expenses [Member]
Defined benefit plan disclosure
Service cost	0	0	0	0
Total non-service cost (benefit)	$ 0	$ 0	$ (1)	$ (1)