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, 2024	Dec. 31, 2023	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 65,326	$ 68,119
Allowance for credit losses		(33)	(34)	$ (28)	$ (34)	$ (28)	$ (37)
Gross Unrealized Gains		847	1,073
Gross Unrealized Losses		(3,807)	(3,916)
Bonds available for sale	[1]	62,333	65,242
Non-Investment Grade
Debt Securities, Available-for-sale [Line Items]
Bonds available for sale		$ 4,800	$ 5,200
Non-Investment Grade | Credit Concentration Risk | Bonds available for sale
Debt Securities, Available-for-sale [Line Items]
Concentration risk (as a percent)		8.00%	8.00%
U.S. government and government sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 4,511	$ 4,444
Allowance for credit losses		0	0
Gross Unrealized Gains		15	40
Gross Unrealized Losses		(117)	(89)
Bonds available for sale		4,409	4,395
Obligations of states, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		4,635	4,930
Allowance for credit losses		0	0
Gross Unrealized Gains		32	60
Gross Unrealized Losses		(175)	(157)
Bonds available for sale		4,492	4,833
Non-U.S. governments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		8,649	8,973
Allowance for credit losses		0	(1)
Gross Unrealized Gains		67	94
Gross Unrealized Losses		(655)	(670)
Bonds available for sale		8,061	8,396
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		32,503	34,013
Allowance for credit losses		(24)	(20)
Gross Unrealized Gains		481	606
Gross Unrealized Losses		(2,173)	(2,253)
Bonds available for sale		30,787	32,346
Mortgage-backed, asset-backed and collateralized
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		15,028	15,759
Allowance for credit losses		(9)	(13)
Gross Unrealized Gains		252	273
Gross Unrealized Losses		(687)	(747)
Bonds available for sale		14,584	15,272
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		6,041	6,423
Allowance for credit losses		(5)	(9)
Gross Unrealized Gains		197	219
Gross Unrealized Losses		(455)	(426)
Bonds available for sale		5,778	6,207
CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		4,431	4,326
Allowance for credit losses		(4)	(4)
Gross Unrealized Gains		19	23
Gross Unrealized Losses		(159)	(198)
Bonds available for sale		4,287	4,147
CLO/ABS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		4,556	5,010
Allowance for credit losses		0	0
Gross Unrealized Gains		36	31
Gross Unrealized Losses		(73)	(123)
Bonds available for sale		$ 4,519	$ 4,918

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