Pension Plans, Retirement Benefits and Savings Plans (Details) - Additional Pension Disclosures - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss):
Total other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss)	$ 87	$ (455)	$ (18)
Pension Plans [Member]
Defined benefit plan disclosure
Total accumulated benefit obligation	3,440	4,250
Aggregate projected benefit obligation for plans with a projected benefit obligation in excess of plan assets	108	131
Aggregate plan assets for plans with a projected benefit obligation in excess of plan assets	0	0
Aggregate accumulated benefit obligation for plans with an accumulated benefit obligation in excess of plan assets	99	118
Aggregate plan assets for plans with an accumulated benefit obligation in excess of plan assets	0	0
Actuarial gain (loss)	845	75
Company contributions	13	12
Components of net periodic benefit cost (benefit)
Service cost	145	141	133
Interest cost on benefit obligation	101	83	114
Expected return on plan assets	(296)	(274)	(275)
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit	(1)	(1)	(1)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss	49	109	93
Total non-service cost (benefit)	(147)	(83)	(69)
Net periodic benefit cost (benefit)	(2)	58	64
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss):
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), prior service benefit	0	0	1
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), net actuarial (gain) loss	174	(338)	61
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), foreign currency exchange rate change	(2)	0	1
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), amortization of prior service benefit	1	1	1
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), amortization of net actuarial gain (loss)	(49)	(109)	(93)
Total other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss)	124	(446)	(29)
Total other changes recognized in net periodic benefit cost and other comprehensive income (loss)	122	(388)	35
Pension Plans [Member] | Net investment income [Member]
Components of net periodic benefit cost (benefit)
Service cost	1	1	1
Total non-service cost (benefit)	(1)	0	0
Pension Plans [Member] | Claims and claim adjustment expenses [Member]
Components of net periodic benefit cost (benefit)
Service cost	58	57	55
Total non-service cost (benefit)	(59)	(34)	(29)
Pension Plans [Member] | General and administrative expenses [Member]
Components of net periodic benefit cost (benefit)
Service cost	86	83	77
Total non-service cost (benefit)	(87)	(49)	(40)
Pension Plans [Member] | United States [Member] | Qualified Plan [Member]
Defined benefit plan disclosure
Total accumulated benefit obligation	3,270	4,000
Actuarial gain (loss)	781	73
Required contributions made	0	0	0
Company contributions	0	0	0
Required contributions during next fiscal year	0
Components of net periodic benefit cost (benefit)
Service cost	137	135
Interest cost on benefit obligation	95	79
Nonqualified and Foreign Pension Plans [Member]
Defined benefit plan disclosure
Total accumulated benefit obligation	170	246
Actuarial gain (loss)	64	2
Company contributions	13	12
Components of net periodic benefit cost (benefit)
Service cost	8	6
Interest cost on benefit obligation	6	4
Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Aggregate accumulated benefit obligation for plans with an accumulated benefit obligation in excess of plan assets	99	149
Aggregate plan assets for plans with an accumulated benefit obligation in excess of plan assets	8	9
Actuarial gain (loss)	45	16
Company contributions	6	7
Components of net periodic benefit cost (benefit)
Service cost	0	0	0
Interest cost on benefit obligation	3	3	4
Expected return on plan assets	0	0	0
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit	(3)	(4)	(3)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss	(4)	(2)	(4)
Total non-service cost (benefit)	(4)	(3)	(3)
Net periodic benefit cost (benefit)	(4)	(3)	(3)
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss):
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), prior service benefit	0	0	0
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), net actuarial (gain) loss	(45)	(16)	4
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), foreign currency exchange rate change	1	0	0
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), amortization of prior service benefit	3	4	3
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), amortization of net actuarial gain (loss)	4	2	4
Total other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss)	(37)	(10)	11
Total other changes recognized in net periodic benefit cost and other comprehensive income (loss)	(41)	(13)	8
Postretirement Benefit Plans [Member] | Net investment income [Member]
Components of net periodic benefit cost (benefit)
Service cost	0	0	0
Total non-service cost (benefit)	0	0	0
Postretirement Benefit Plans [Member] | Claims and claim adjustment expenses [Member]
Components of net periodic benefit cost (benefit)
Service cost	0	0	0
Total non-service cost (benefit)	(2)	(1)	(1)
Postretirement Benefit Plans [Member] | General and administrative expenses [Member]
Components of net periodic benefit cost (benefit)
Service cost	0	0	0
Total non-service cost (benefit)	$ (2)	$ (2)	$ (2)