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Investments - Fixed Maturity Securities and Short Term Investments (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Percent of Total	100.00%		100.00%
Amortized Cost	$ 6,492		$ 6,827
Allowance for Credit Losses	(54)	$ (47)	(60)	$ (66)	$ (69)	$ (77)
Gross Unrealized Gains	130		44
Gross Unrealized Losses	(290)		(442)
Estimated Fair Value	$ 6,278		$ 6,369
Government agency obligations as a percentage of total mortgage backed securities	74.00%		68.00%
Obligations of state and political subdivisions
Schedule of Investments [Line Items]
Percent of Total	28.00%		30.00%
Amortized Cost	$ 1,808		$ 2,032
Allowance for Credit Losses	(13)		(14)
Gross Unrealized Gains	36		25
Gross Unrealized Losses	(76)		(103)
Estimated Fair Value	$ 1,755		$ 1,940
U.S. government and agencies
Schedule of Investments [Line Items]
Percent of Total	1.00%		1.00%
Amortized Cost	$ 51		$ 72
Allowance for Credit Losses	0		0
Gross Unrealized Gains	1		1
Gross Unrealized Losses	(4)		(6)
Estimated Fair Value	$ 48		$ 67
Corporate securities
Schedule of Investments [Line Items]
Percent of Total	46.00%		38.00%
Amortized Cost	$ 2,977		$ 2,586
Allowance for Credit Losses	(7)		(7)
Gross Unrealized Gains	73		9
Gross Unrealized Losses	(120)		(206)
Estimated Fair Value	$ 2,923		$ 2,382
RMBS
Schedule of Investments [Line Items]
Percent of Total	10.00%		9.00%
Amortized Cost	$ 670		$ 657
Allowance for Credit Losses	(24)		(21)
Gross Unrealized Gains	8		2
Gross Unrealized Losses	(51)		(71)
Estimated Fair Value	$ 603		$ 567
CMBS
Schedule of Investments [Line Items]
Percent of Total	3.00%		3.00%
Amortized Cost	$ 184		$ 189
Allowance for Credit Losses	0		0
Gross Unrealized Gains	2		0
Gross Unrealized Losses	(1)		(3)
Estimated Fair Value	$ 185		$ 186
CLOs
Schedule of Investments [Line Items]
Percent of Total	8.00%		9.00%
Amortized Cost	$ 506		$ 615
Allowance for Credit Losses	(10)		(1)
Gross Unrealized Gains	5		6
Gross Unrealized Losses	(29)		(9)
Estimated Fair Value	$ 472		$ 611
Others
Schedule of Investments [Line Items]
Percent of Total	3.00%		9.00%
Amortized Cost	$ 196		$ 593
Allowance for Credit Losses	0		(17)
Gross Unrealized Gains	3		1
Gross Unrealized Losses	0		(30)
Estimated Fair Value	199		547
Others | Affiliated Entity
Schedule of Investments [Line Items]
Amortized Cost	48		41
Estimated Fair Value	$ 49		$ 42
Non-U.S. government securities
Schedule of Investments [Line Items]
Percent of Total	1.00%		1.00%
Amortized Cost	$ 100		$ 83
Allowance for Credit Losses	0		0
Gross Unrealized Gains	2		0
Gross Unrealized Losses	(9)		(14)
Estimated Fair Value	$ 93		$ 69

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