Investments - Available for Sale Securities in Continuous Unrealized Loss Position (Details) $ in Millions	Jun. 30, 2025 USD ($) security	Dec. 31, 2024 USD ($) security
Fair Value
Fair Value, Less than 12 Months	$ 12,522	$ 21,662
Fair Value, 12 Months or More	14,491	18,751
Fair Value, Total	27,013	40,413
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	317	428
Gross Unrealized Losses, 12 Months or More	2,007	2,655
Gross Unrealized Losses, Total	$ 2,324	$ 3,083
Number of securities in an unrealized loss position | security	8,797	12,274
Number of individual securities in continuous unrealized loss position for longer than twelve months | security	4,762	5,984
U.S. government and government sponsored entities
Fair Value
Fair Value, Less than 12 Months	$ 491	$ 1,718
Fair Value, 12 Months or More	350	358
Fair Value, Total	841	2,076
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	13	21
Gross Unrealized Losses, 12 Months or More	75	78
Gross Unrealized Losses, Total	88	99
Obligations of states, municipalities and political subdivisions
Fair Value
Fair Value, Less than 12 Months	647	1,502
Fair Value, 12 Months or More	570	586
Fair Value, Total	1,217	2,088
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	15	33
Gross Unrealized Losses, 12 Months or More	61	79
Gross Unrealized Losses, Total	76	112
Non-U.S. governments
Fair Value
Fair Value, Less than 12 Months	1,637	1,964
Fair Value, 12 Months or More	1,532	3,446
Fair Value, Total	3,169	5,410
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	52	55
Gross Unrealized Losses, 12 Months or More	371	534
Gross Unrealized Losses, Total	423	589
Corporate debt
Fair Value
Fair Value, Less than 12 Months	6,463	10,347
Fair Value, 12 Months or More	9,283	10,907
Fair Value, Total	15,746	21,254
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	188	234
Gross Unrealized Losses, 12 Months or More	1,157	1,515
Gross Unrealized Losses, Total	1,345	1,749
RMBS
Fair Value
Fair Value, Less than 12 Months	1,571	3,711
Fair Value, 12 Months or More	1,840	2,147
Fair Value, Total	3,411	5,858
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	37	58
Gross Unrealized Losses, 12 Months or More	280	343
Gross Unrealized Losses, Total	317	401
CMBS
Fair Value
Fair Value, Less than 12 Months	521	1,052
Fair Value, 12 Months or More	642	992
Fair Value, Total	1,163	2,044
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	5	18
Gross Unrealized Losses, 12 Months or More	41	71
Gross Unrealized Losses, Total	46	89
CLO/ABS
Fair Value
Fair Value, Less than 12 Months	1,192	1,368
Fair Value, 12 Months or More	274	315
Fair Value, Total	1,466	1,683
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	7	9
Gross Unrealized Losses, 12 Months or More	22	35
Gross Unrealized Losses, Total	$ 29	$ 44