Investments - Securities available for sale in a loss position (Details) $ in Millions	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Fair Value
Fair Value, Less than 12 Months	$ 34,407	$ 173,000
Fair Value, 12 Months or More	136,774	23,486
Fair Value, Total	171,181	196,486
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	2,958	26,605
Gross Unrealized Losses, 12 Months or More	21,333	5,132
Gross Unrealized Losses, Total	$ 24,291	$ 31,737
Number of securities in an unrealized loss position | security	27,930	36,549
Number of individual securities in continuous unrealized loss position for longer than twelve months | security	22,663	4,048
U.S. government and government sponsored entities
Fair Value
Fair Value, Less than 12 Months	$ 1,046	$ 3,493
Fair Value, 12 Months or More	1,550	1,816
Fair Value, Total	2,596	5,309
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	12	368
Gross Unrealized Losses, 12 Months or More	315	128
Gross Unrealized Losses, Total	327	496
Obligations of states, municipalities and political subdivisions
Fair Value
Fair Value, Less than 12 Months	1,994	8,697
Fair Value, 12 Months or More	5,218	73
Fair Value, Total	7,212	8,770
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	133	1,180
Gross Unrealized Losses, 12 Months or More	709	15
Gross Unrealized Losses, Total	842	1,195
Non-U.S. governments
Fair Value
Fair Value, Less than 12 Months	1,901	10,702
Fair Value, 12 Months or More	7,483	779
Fair Value, Total	9,384	11,481
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	168	1,526
Gross Unrealized Losses, 12 Months or More	1,175	191
Gross Unrealized Losses, Total	1,343	1,717
Corporate debt
Fair Value
Fair Value, Less than 12 Months	15,483	110,683
Fair Value, 12 Months or More	93,649	13,778
Fair Value, Total	109,132	124,461
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	1,936	19,756
Gross Unrealized Losses, 12 Months or More	16,076	3,609
Gross Unrealized Losses, Total	18,012	23,365
RMBS
Fair Value
Fair Value, Less than 12 Months	4,154	10,953
Fair Value, 12 Months or More	7,246	1,005
Fair Value, Total	11,400	11,958
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	288	1,293
Gross Unrealized Losses, 12 Months or More	880	182
Gross Unrealized Losses, Total	1,168	1,475
CMBS
Fair Value
Fair Value, Less than 12 Months	2,864	11,620
Fair Value, 12 Months or More	8,192	1,728
Fair Value, Total	11,056	13,348
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	219	1,094
Gross Unrealized Losses, 12 Months or More	1,027	326
Gross Unrealized Losses, Total	1,246	1,420
CLO/ABS
Fair Value
Fair Value, Less than 12 Months	6,965	16,852
Fair Value, 12 Months or More	13,436	4,307
Fair Value, Total	20,401	21,159
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	202	1,388
Gross Unrealized Losses, 12 Months or More	1,151	681
Gross Unrealized Losses, Total	$ 1,353	$ 2,069