Investments - Available for Sale Securities in Continuous Unrealized Loss Position (Details) $ in Millions	Jun. 30, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Fair Value
Fair Value, Less than 12 Months	$ 13,886	$ 11,248
Fair Value, 12 Months or More	30,118	31,037
Fair Value, Total	44,004	42,285
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	291	493
Gross Unrealized Losses, 12 Months or More	3,490	3,392
Gross Unrealized Losses, Total	$ 3,781	$ 3,885
Number of securities in an unrealized loss position | security	13,477	13,052
Number of individual securities in continuous unrealized loss position for longer than twelve months | security	9,923	10,027
U.S. government and government sponsored entities
Fair Value
Fair Value, Less than 12 Months	$ 2,137	$ 1,027
Fair Value, 12 Months or More	1,274	804
Fair Value, Total	3,411	1,831
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	20	10
Gross Unrealized Losses, 12 Months or More	97	79
Gross Unrealized Losses, Total	117	89
Obligations of states, municipalities and political subdivisions
Fair Value
Fair Value, Less than 12 Months	1,529	850
Fair Value, 12 Months or More	1,904	1,602
Fair Value, Total	3,433	2,452
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	31	24
Gross Unrealized Losses, 12 Months or More	144	133
Gross Unrealized Losses, Total	175	157
Non-U.S. governments
Fair Value
Fair Value, Less than 12 Months	1,492	1,431
Fair Value, 12 Months or More	4,504	4,503
Fair Value, Total	5,996	5,934
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	44	87
Gross Unrealized Losses, 12 Months or More	611	583
Gross Unrealized Losses, Total	655	670
Corporate debt
Fair Value
Fair Value, Less than 12 Months	5,683	4,089
Fair Value, 12 Months or More	16,911	18,612
Fair Value, Total	22,594	22,701
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	112	171
Gross Unrealized Losses, 12 Months or More	2,050	2,070
Gross Unrealized Losses, Total	2,162	2,241
RMBS
Fair Value
Fair Value, Less than 12 Months	1,114	1,456
Fair Value, 12 Months or More	2,752	2,385
Fair Value, Total	3,866	3,841
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	48	114
Gross Unrealized Losses, 12 Months or More	398	300
Gross Unrealized Losses, Total	446	414
CMBS
Fair Value
Fair Value, Less than 12 Months	999	1,024
Fair Value, 12 Months or More	1,991	1,622
Fair Value, Total	2,990	2,646
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	17	54
Gross Unrealized Losses, 12 Months or More	136	137
Gross Unrealized Losses, Total	153	191
CLO/ABS
Fair Value
Fair Value, Less than 12 Months	932	1,371
Fair Value, 12 Months or More	782	1,509
Fair Value, Total	1,714	2,880
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	19	33
Gross Unrealized Losses, 12 Months or More	54	90
Gross Unrealized Losses, Total	$ 73	$ 123