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Investments - Gross Unrealized Loss by Length of Time (Details) $ in Millions	Sep. 30, 2025 USD ($) security	Dec. 31, 2024 USD ($) security
Less than 12 months
Fair Value	$ 598	$ 1,975
Gross Unrealized Loss	$ (11)	$ (40)
Number of securities | security	194	569
12 months or more
Fair Value	$ 1,945	$ 2,417
Gross Unrealized Loss	$ (188)	$ (277)
Number of securities | security	905	1,065
Total
Fair Value	$ 2,543	$ 4,392
Gross Unrealized Loss	$ (199)	$ (317)
Number of securities | security	1,083	1,591
Obligations of state and political subdivisions
Less than 12 months
Fair Value	$ 193	$ 624
Gross Unrealized Loss	(2)	(7)
12 months or more
Fair Value	822	964
Gross Unrealized Loss	(74)	(96)
Total
Fair Value	1,015	1,588
Gross Unrealized Loss	(76)	(103)
U.S. government and agencies
Less than 12 months
Fair Value	5	5
Gross Unrealized Loss	0	0
12 months or more
Fair Value	12	28
Gross Unrealized Loss	(4)	(6)
Total
Fair Value	17	33
Gross Unrealized Loss	(4)	(6)
Corporate securities
Less than 12 months
Fair Value	150	762
Gross Unrealized Loss	(1)	(20)
12 months or more
Fair Value	858	1,046
Gross Unrealized Loss	(93)	(150)
Total
Fair Value	1,008	1,808
Gross Unrealized Loss	(94)	(170)
RMBS
Less than 12 months
Fair Value	20	255
Gross Unrealized Loss	0	(4)
12 months or more
Fair Value	131	123
Gross Unrealized Loss	(7)	(10)
Total
Fair Value	151	378
Gross Unrealized Loss	(7)	(14)
CMBS
Less than 12 months
Fair Value	36	83
Gross Unrealized Loss	0	0
12 months or more
Fair Value	59	103
Gross Unrealized Loss	(1)	(3)
Total
Fair Value	95	186
Gross Unrealized Loss	(1)	(3)
CLOs
Less than 12 months
Fair Value	128	151
Gross Unrealized Loss	(8)	(5)
12 months or more
Fair Value	34	107
Gross Unrealized Loss	0	(1)
Total
Fair Value	162	258
Gross Unrealized Loss	(8)	(6)
Others
Less than 12 months
Fair Value	34	60
Gross Unrealized Loss	0	(1)
12 months or more
Fair Value	10	16
Gross Unrealized Loss	0	0
Total
Fair Value	44	76
Gross Unrealized Loss	0	(1)
Non-U.S. government securities
Less than 12 months
Fair Value	32	35
Gross Unrealized Loss	0	(3)
12 months or more
Fair Value	19	30
Gross Unrealized Loss	(9)	(11)
Total
Fair Value	51	65
Gross Unrealized Loss	$ (9)	$ (14)

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