Pension Plans, Retirement Benefits and Savings Plans (Details) - Additional Pension Disclosures - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
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)	$ (296)	$ (106)	$ 87
Pension Plans [Member]
Defined benefit plan disclosure
Total accumulated benefit obligation	3,270	3,470
Aggregate projected benefit obligation for plans with a projected benefit obligation in excess of plan assets	118	114
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	112	106
Aggregate plan assets for plans with an accumulated benefit obligation in excess of plan assets	0	0
Actuarial gain (loss)	155	(124)
Company contributions	12	13
Components of net periodic benefit cost (benefit)
Service cost	116	108	145
Interest cost on benefit obligation	172	176	101
Expected return on plan assets	(298)	(311)	(296)
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit	0	(1)	(1)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss	7	0	49
Total non-service cost (benefit)	(119)	(136)	(147)
Net periodic benefit cost (benefit)	(3)	(28)	(2)
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	(274)	(114)	174
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), foreign currency exchange rate change	0	0	(2)
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), amortization of prior service benefit	0	1	1
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), amortization of net actuarial gain (loss)	(7)	0	(49)
Total other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss)	(281)	(113)	124
Total other changes recognized in net periodic benefit cost (benefit) and other comprehensive income (loss)	(284)	(141)	122
Pension Plans [Member] | Net investment income [Member]
Components of net periodic benefit cost (benefit)
Service cost	1	0	1
Total non-service cost (benefit)	(1)	(1)	(1)
Pension Plans [Member] | Claims and claim adjustment expenses [Member]
Components of net periodic benefit cost (benefit)
Service cost	45	44	58
Total non-service cost (benefit)	(45)	(54)	(59)
Pension Plans [Member] | General and administrative expenses [Member]
Components of net periodic benefit cost (benefit)
Service cost	70	64	86
Total non-service cost (benefit)	(73)	(81)	(87)
Pension Plans [Member] | Nonqualified and Foreign Pension Plans [Member]
Defined benefit plan disclosure
Total accumulated benefit obligation	180	176
Actuarial gain (loss)	(4)	(1)
Company contributions	12	13
Components of net periodic benefit cost (benefit)
Service cost	5	4
Interest cost on benefit obligation	9	9
Pension Plans [Member] | United States [Member] | Qualified Plan [Member]
Defined benefit plan disclosure
Total accumulated benefit obligation	3,090	3,300
Actuarial gain (loss)	159	(123)
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	111	104
Interest cost on benefit obligation	163	167
Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Aggregate accumulated benefit obligation for plans with an accumulated benefit obligation in excess of plan assets	62	92
Aggregate plan assets for plans with an accumulated benefit obligation in excess of plan assets	6	7
Actuarial gain (loss)	28	6
Company contributions	4	5
Components of net periodic benefit cost (benefit)
Service cost	0	0	0
Interest cost on benefit obligation	4	5	3
Expected return on plan assets	0	0	0
Net periodic benefit cost (benefit), amortization of unrecognized prior service benefit	(3)	(3)	(3)
Net periodic benefit cost (benefit), amortization of unrecognized net actuarial (gain) loss	(9)	(9)	(4)
Total non-service cost (benefit)	(8)	(7)	(4)
Net periodic benefit cost (benefit)	(8)	(7)	(4)
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	(28)	(6)	(45)
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), foreign currency exchange rate change	1	0	1
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), amortization of prior service benefit	3	3	3
Other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss), amortization of net actuarial gain (loss)	9	9	4
Total other changes in benefit plan assets and benefit obligations recognized in other comprehensive income (loss)	(15)	6	(37)
Total other changes recognized in net periodic benefit cost (benefit) and other comprehensive income (loss)	(23)	(1)	(41)
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)	(3)	(3)	(2)
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)	$ (5)	$ (4)	$ (2)