Investments - Amortized cost or cost and fair value of available for sale securities (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2023	Dec. 31, 2022	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 249,235	$ 255,993
Allowance for credit losses		(125)	(186)	$ (136)	$ (175)	$ (191)	$ (98)
Gross Unrealized Gains		2,311	2,222
Gross Unrealized Losses		(28,891)	(31,873)
Bonds available for sale	[1]	222,530	226,156
Non-Investment Grade
Debt Securities, Available-for-sale [Line Items]
Bonds available for sale		$ 17,800	$ 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		$ 6,485	$ 7,094
Allowance for credit losses		0	0
Gross Unrealized Gains		17	21
Gross Unrealized Losses		(333)	(496)
Bonds available for sale		6,169	6,619
Obligations of states, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		11,982	13,195
Allowance for credit losses		0	0
Gross Unrealized Gains		107	99
Gross Unrealized Losses		(943)	(1,195)
Bonds available for sale		11,146	12,099
Non-U.S. governments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		14,087	15,133
Allowance for credit losses		(11)	(6)
Gross Unrealized Gains		97	91
Gross Unrealized Losses		(1,665)	(1,733)
Bonds available for sale		12,508	13,485
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		153,633	160,242
Allowance for credit losses		(67)	(132)
Gross Unrealized Gains		1,122	1,152
Gross Unrealized Losses		(21,385)	(23,423)
Bonds available for sale		133,303	137,839
Mortgage-backed, asset-backed and collateralized
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		63,048	60,329
Allowance for credit losses		(47)	(48)
Gross Unrealized Gains		968	859
Gross Unrealized Losses		(4,565)	(5,026)
Bonds available for sale		59,404	56,114
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		19,353	19,584
Allowance for credit losses		(26)	(37)
Gross Unrealized Gains		856	807
Gross Unrealized Losses		(1,289)	(1,537)
Bonds available for sale		18,894	18,817
CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		15,258	15,610
Allowance for credit losses		(19)	(11)
Gross Unrealized Gains		13	14
Gross Unrealized Losses		(1,503)	(1,420)
Bonds available for sale		13,749	14,193
CLO/ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		28,437	25,135
Allowance for credit losses		(2)	0
Gross Unrealized Gains		99	38
Gross Unrealized Losses		(1,773)	(2,069)
Bonds available for sale		$ 26,761	$ 23,104

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