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Investments - Gross Unrealized Loss by Length of Time (Details) $ in Millions	Jun. 30, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Less than 12 months
Fair Value	$ 1,205	$ 766
Gross Unrealized Loss	$ (9)	$ (7)
Number of securities | security	395	274
12 months or more
Fair Value	$ 3,104	$ 3,162
Gross Unrealized Loss	$ (311)	$ (281)
Number of securities | security	1,291	1,266
Total
Fair Value	$ 4,309	$ 3,928
Gross Unrealized Loss	$ (320)	$ (288)
Number of securities | security	1,668	1,525
Obligations of state and political subdivisions
Less than 12 months
Fair Value	$ 572	$ 641
Gross Unrealized Loss	(4)	(4)
12 months or more
Fair Value	1,231	931
Gross Unrealized Loss	(100)	(87)
Total
Fair Value	1,803	1,572
Gross Unrealized Loss	(104)	(91)
U.S. government and agencies
Less than 12 months
Fair Value	28	0
Gross Unrealized Loss	0	0
12 months or more
Fair Value	33	33
Gross Unrealized Loss	(6)	(6)
Total
Fair Value	61	33
Gross Unrealized Loss	(6)	(6)
Corporate securities
Less than 12 months
Fair Value	332	72
Gross Unrealized Loss	(3)	(1)
12 months or more
Fair Value	1,316	1,426
Gross Unrealized Loss	(170)	(152)
Total
Fair Value	1,648	1,498
Gross Unrealized Loss	(173)	(153)
RMBS
Less than 12 months
Fair Value	147	27
Gross Unrealized Loss	(1)	(1)
12 months or more
Fair Value	141	124
Gross Unrealized Loss	(12)	(8)
Total
Fair Value	288	151
Gross Unrealized Loss	(13)	(9)
CMBS
Less than 12 months
Fair Value	28	3
Gross Unrealized Loss	0	0
12 months or more
Fair Value	116	148
Gross Unrealized Loss	(6)	(6)
Total
Fair Value	144	151
Gross Unrealized Loss	(6)	(6)
CLOs
Less than 12 months
Fair Value	32	22
Gross Unrealized Loss	0	(1)
12 months or more
Fair Value	178	379
Gross Unrealized Loss	(1)	(6)
Total
Fair Value	210	401
Gross Unrealized Loss	(1)	(7)
Other
Less than 12 months
Fair Value	66	1
Gross Unrealized Loss	(1)	0
12 months or more
Fair Value	23	26
Gross Unrealized Loss	(1)	(1)
Total
Fair Value	89	27
Gross Unrealized Loss	(2)	(1)
Non-U.S. government securities
Less than 12 months
Fair Value	0	0
Gross Unrealized Loss	0	0
12 months or more
Fair Value	66	95
Gross Unrealized Loss	(15)	(15)
Total
Fair Value	66	95
Gross Unrealized Loss	$ (15)	$ (15)

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