Investments - Fixed Maturity Securities and Short Term Investments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Percent of Total	100.00%		100.00%
Amortized Cost	$ 6,971		$ 7,707
Allowance for Credit Losses	(86)	$ (79)	(65)	$ (57)	$ (51)	$ (42)
Gross Unrealized Gains	30		65
Gross Unrealized Losses	(648)		(588)
Estimated Fair Value	$ 6,267		$ 7,119
Government agency obligations as a percentage of total mortgage backed securities	38.00%		30.00%
Obligations of state and political subdivisions
Schedule of Investments [Line Items]
Percent of Total	42.00%		45.00%
Amortized Cost	$ 2,938		$ 3,509
Allowance for Credit Losses	(14)		(14)
Gross Unrealized Gains	20		37
Gross Unrealized Losses	(178)		(138)
Estimated Fair Value	$ 2,766		$ 3,394
U.S. government and agencies
Schedule of Investments [Line Items]
Percent of Total	1.00%		2.00%
Amortized Cost	$ 65		$ 118
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		1
Gross Unrealized Losses	(7)		(8)
Estimated Fair Value	$ 58		$ 111
Corporate securities
Schedule of Investments [Line Items]
Percent of Total	33.00%		31.00%
Amortized Cost	$ 2,321		$ 2,387
Allowance for Credit Losses	(6)		(6)
Gross Unrealized Gains	1		2
Gross Unrealized Losses	(307)		(299)
Estimated Fair Value	$ 2,009		$ 2,084
RMBS
Schedule of Investments [Line Items]
Percent of Total	6.00%		5.00%
Amortized Cost	$ 430		$ 418
Allowance for Credit Losses	(20)		(19)
Gross Unrealized Gains	2		3
Gross Unrealized Losses	(82)		(62)
Estimated Fair Value	$ 330		$ 340
CMBS
Schedule of Investments [Line Items]
Percent of Total	3.00%		4.00%
Amortized Cost	$ 198		$ 282
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(10)		(11)
Estimated Fair Value	$ 188		$ 271
CLOs
Schedule of Investments [Line Items]
Percent of Total	7.00%		6.00%
Amortized Cost	$ 463		$ 449
Allowance for Credit Losses	0		0
Gross Unrealized Gains	1		0
Gross Unrealized Losses	(10)		(21)
Estimated Fair Value	$ 454		$ 428
Others
Schedule of Investments [Line Items]
Percent of Total	6.00%		5.00%
Amortized Cost	$ 440		$ 423
Allowance for Credit Losses	(46)		(26)
Gross Unrealized Gains	6		22
Gross Unrealized Losses	(31)		(26)
Estimated Fair Value	$ 369		$ 393
Non-U.S. government securities
Schedule of Investments [Line Items]
Percent of Total	2.00%		2.00%
Amortized Cost	$ 116		$ 121
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(23)		(23)
Estimated Fair Value	$ 93		$ 98