Investments - Fixed Maturity Securities and Short Term Investments (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Percent of Total	100.00%	100.00%
Amortized Cost	$ 6,553	$ 6,746
Allowance for Credit Losses	(67)	(77)	$ (69)	$ (65)
Gross Unrealized Gains	43	55
Gross Unrealized Losses	(438)	(417)
Estimated Fair Value	$ 6,091	$ 6,307
Government agency obligations as a percentage of total mortgage backed securities	56.00%	42.00%
Obligations of state and political subdivisions
Schedule of Investments [Line Items]
Percent of Total	37.00%	41.00%
Amortized Cost	$ 2,418	$ 2,733
Allowance for Credit Losses	(14)	(13)
Gross Unrealized Gains	27	33
Gross Unrealized Losses	(100)	(92)
Estimated Fair Value	$ 2,331	$ 2,661
U.S. government and agencies
Schedule of Investments [Line Items]
Percent of Total	1.00%	1.00%
Amortized Cost	$ 60	$ 65
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(6)	(6)
Estimated Fair Value	$ 55	$ 60
Corporate securities
Schedule of Investments [Line Items]
Percent of Total	35.00%	34.00%
Amortized Cost	$ 2,307	$ 2,327
Allowance for Credit Losses	(6)	(6)
Gross Unrealized Gains	10	17
Gross Unrealized Losses	(210)	(197)
Estimated Fair Value	$ 2,101	$ 2,141
RMBS
Schedule of Investments [Line Items]
Percent of Total	7.00%	6.00%
Amortized Cost	$ 490	$ 428
Allowance for Credit Losses	(22)	(21)
Gross Unrealized Gains	3	3
Gross Unrealized Losses	(69)	(68)
Estimated Fair Value	$ 402	$ 342
CMBS
Schedule of Investments [Line Items]
Percent of Total	3.00%	2.00%
Amortized Cost	$ 202	$ 157
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	(6)
Estimated Fair Value	$ 196	$ 151
CLOs
Schedule of Investments [Line Items]
Percent of Total	7.00%	7.00%
Amortized Cost	$ 442	$ 456
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(4)	(7)
Estimated Fair Value	$ 439	$ 450
Others
Schedule of Investments [Line Items]
Percent of Total	8.00%	7.00%
Amortized Cost	$ 535	$ 465
Allowance for Credit Losses	(25)	(37)
Gross Unrealized Gains	1	0
Gross Unrealized Losses	(28)	(26)
Estimated Fair Value	$ 483	$ 402
Non-U.S. government securities
Schedule of Investments [Line Items]
Percent of Total	2.00%	2.00%
Amortized Cost	$ 99	$ 115
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(15)	(15)
Estimated Fair Value	$ 84	$ 100