Investments - Securities available for sale in a loss position (Details) $ in Millions	Sep. 30, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Fair Value
Fair Value, Less than 12 Months	$ 95,208	$ 173,000
Fair Value, 12 Months or More	94,317	23,486
Fair Value, Total	189,525	196,486
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	14,611	26,605
Gross Unrealized Losses, 12 Months or More	20,764	5,132
Gross Unrealized Losses, Total	$ 35,375	$ 31,737
Number of securities in an unrealized loss position \| security	32,663	36,549
Number of individual securities in continuous unrealized loss position for longer than twelve months \| security	17,596	4,048
U.S. government and government sponsored entities
Fair Value
Fair Value, Less than 12 Months	$ 4,708	$ 3,493
Fair Value, 12 Months or More	816	1,816
Fair Value, Total	5,524	5,309
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	307	368
Gross Unrealized Losses, 12 Months or More	199	128
Gross Unrealized Losses, Total	506	496
Obligations of states, municipalities and political subdivisions
Fair Value
Fair Value, Less than 12 Months	5,378	8,697
Fair Value, 12 Months or More	4,099	73
Fair Value, Total	9,477	8,770
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	589	1,180
Gross Unrealized Losses, 12 Months or More	785	15
Gross Unrealized Losses, Total	1,374	1,195
Non-U.S. governments
Fair Value
Fair Value, Less than 12 Months	6,831	10,702
Fair Value, 12 Months or More	3,578	779
Fair Value, Total	10,409	11,481
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	965	1,526
Gross Unrealized Losses, 12 Months or More	928	191
Gross Unrealized Losses, Total	1,893	1,717
Corporate debt
Fair Value
Fair Value, Less than 12 Months	53,646	110,683
Fair Value, 12 Months or More	62,852	13,778
Fair Value, Total	116,498	124,461
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	10,739	19,756
Gross Unrealized Losses, 12 Months or More	15,812	3,609
Gross Unrealized Losses, Total	26,551	23,365
RMBS
Fair Value
Fair Value, Less than 12 Months	7,529	10,953
Fair Value, 12 Months or More	5,481	1,005
Fair Value, Total	13,010	11,958
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	705	1,293
Gross Unrealized Losses, 12 Months or More	961	182
Gross Unrealized Losses, Total	1,666	1,475
CMBS
Fair Value
Fair Value, Less than 12 Months	6,322	11,620
Fair Value, 12 Months or More	5,851	1,728
Fair Value, Total	12,173	13,348
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	770	1,094
Gross Unrealized Losses, 12 Months or More	860	326
Gross Unrealized Losses, Total	1,630	1,420
CLO/ABS
Fair Value
Fair Value, Less than 12 Months	10,794	16,852
Fair Value, 12 Months or More	11,640	4,307
Fair Value, Total	22,434	21,159
Gross Unrealized Losses
Gross Unrealized Losses, Less than 12 Months	536	1,388
Gross Unrealized Losses, 12 Months or More	1,219	681
Gross Unrealized Losses, Total	$ 1,755	$ 2,069

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