Investments - Amortized cost or cost and fair value of available for sale securities (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2023	Dec. 31, 2022	Jun. 30, 2023	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 248,691	$ 255,993
Allowance for credit losses		(138)	(186)	$ (125)	$ (115)	$ (175)	$ (98)
Gross Unrealized Gains		1,881	2,222
Gross Unrealized Losses		(35,494)	(31,873)
Bonds available for sale	[1]	214,940	226,156
Non-Investment Grade
Debt Securities, Available-for-sale [Line Items]
Bonds available for sale		$ 17,400	$ 22,300
Non-Investment Grade | Credit Concentration Risk | Bonds available for sale
Debt Securities, Available-for-sale [Line Items]
Concentration risk, percentage		8.00%	10.00%
U.S. government and government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 6,456	$ 7,094
Allowance for credit losses		0	0
Gross Unrealized Gains		4	21
Gross Unrealized Losses		(506)	(496)
Bonds available for sale		5,954	6,619
Obligations of states, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		11,781	13,195
Allowance for credit losses		0	0
Gross Unrealized Gains		39	99
Gross Unrealized Losses		(1,374)	(1,195)
Bonds available for sale		10,446	12,099
Non-U.S. governments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		13,559	15,133
Allowance for credit losses		(4)	(6)
Gross Unrealized Gains		68	91
Gross Unrealized Losses		(1,899)	(1,733)
Bonds available for sale		11,724	13,485
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		151,989	160,242
Allowance for credit losses		(87)	(132)
Gross Unrealized Gains		806	1,152
Gross Unrealized Losses		(26,617)	(23,423)
Bonds available for sale		126,091	137,839
Mortgage-backed, asset-backed and collateralized
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		64,906	60,329
Allowance for credit losses		(47)	(48)
Gross Unrealized Gains		964	859
Gross Unrealized Losses		(5,098)	(5,026)
Bonds available for sale		60,725	56,114
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		19,643	19,584
Allowance for credit losses		(33)	(37)
Gross Unrealized Gains		826	807
Gross Unrealized Losses		(1,705)	(1,537)
Bonds available for sale		18,731	18,817
CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		15,143	15,610
Allowance for credit losses		(13)	(11)
Gross Unrealized Gains		18	14
Gross Unrealized Losses		(1,638)	(1,420)
Bonds available for sale		13,510	14,193
CLO/ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		30,120	25,135
Allowance for credit losses		(1)	0
Gross Unrealized Gains		120	38
Gross Unrealized Losses		(1,755)	(2,069)
Bonds available for sale		$ 28,484	$ 23,104

[1] See Note 10 for details of balances associated with variable interest entities.