Pension Plans, Retirement Benefits and Savings Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Pension Plans [Member]
Defined benefit plan disclosure
Service cost	$ 36	$ 35	$ 109	$ 106
Interest cost on benefit obligation	25	21	76	62
Expected return on plan assets	(74)	(69)	(222)	(206)
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit	0	(1)	0	(1)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss	12	28	37	82
Total non-service cost (benefit)	(37)	(21)	(109)	(63)
Net periodic benefit cost (benefit)	(1)	14	0	43
Pension Plans [Member] | Claims and claim adjustment expenses [Member]
Defined benefit plan disclosure
Service cost	14	14	44	43
Total non-service cost (benefit)	(15)	(9)	(44)	(26)
Pension Plans [Member] | General and administrative expenses [Member]
Defined benefit plan disclosure
Service cost	22	21	65	63
Total non-service cost (benefit)	(22)	(12)	(65)	(37)
Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Service cost	0	0	0	0
Interest cost on benefit obligation	0	1	2	2
Expected return on plan assets	0	0	0	0
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit	0	(1)	(2)	(3)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss	(1)	(1)	(3)	(2)
Total non-service cost (benefit)	(1)	(1)	(3)	(3)
Net periodic benefit cost (benefit)	(1)	(1)	(3)	(3)
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)	0	0	(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)	$ (1)	$ (1)	$ (2)	$ (2)