Investments - Available for Sale Securities in Continuous Unrealized Loss Position (Details) $ in Millions	Sep. 30, 2025 USD ($) security	Dec. 31, 2024 USD ($) security
Fair Value
Fair Value, Less than 12 Months	$ 9,168	$ 21,662
Fair Value, 12 Months or More	13,778	18,751
Fair Value, Total	22,946	40,413
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	192	428
Gross Unrealized Losses, 12 Months or More	1,777	2,655
Gross Unrealized Losses, Total	$ 1,969	$ 3,083
Number of securities in an unrealized loss position | security	7,530	12,274
Number of individual securities in continuous unrealized loss position for longer than twelve months | security	4,415	5,984
U.S. government and government sponsored entities
Fair Value
Fair Value, Less than 12 Months	$ 331	$ 1,718
Fair Value, 12 Months or More	325	358
Fair Value, Total	656	2,076
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	10	21
Gross Unrealized Losses, 12 Months or More	74	78
Gross Unrealized Losses, Total	84	99
Obligations of states, municipalities and political subdivisions
Fair Value
Fair Value, Less than 12 Months	248	1,502
Fair Value, 12 Months or More	543	586
Fair Value, Total	791	2,088
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	8	33
Gross Unrealized Losses, 12 Months or More	50	79
Gross Unrealized Losses, Total	58	112
Non-U.S. governments
Fair Value
Fair Value, Less than 12 Months	1,262	1,964
Fair Value, 12 Months or More	1,311	3,446
Fair Value, Total	2,573	5,410
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	28	55
Gross Unrealized Losses, 12 Months or More	344	534
Gross Unrealized Losses, Total	372	589
Corporate debt
Fair Value
Fair Value, Less than 12 Months	5,027	10,347
Fair Value, 12 Months or More	8,729	10,907
Fair Value, Total	13,756	21,254
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	116	234
Gross Unrealized Losses, 12 Months or More	1,002	1,515
Gross Unrealized Losses, Total	1,118	1,749
RMBS
Fair Value
Fair Value, Less than 12 Months	781	3,711
Fair Value, 12 Months or More	2,090	2,147
Fair Value, Total	2,871	5,858
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	19	58
Gross Unrealized Losses, 12 Months or More	258	343
Gross Unrealized Losses, Total	277	401
CMBS
Fair Value
Fair Value, Less than 12 Months	537	1,052
Fair Value, 12 Months or More	528	992
Fair Value, Total	1,065	2,044
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	5	18
Gross Unrealized Losses, 12 Months or More	33	71
Gross Unrealized Losses, Total	38	89
CLO/ABS
Fair Value
Fair Value, Less than 12 Months	982	1,368
Fair Value, 12 Months or More	252	315
Fair Value, Total	1,234	1,683
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	6	9
Gross Unrealized Losses, 12 Months or More	16	35
Gross Unrealized Losses, Total	$ 22	$ 44