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Investments - Gross Unrealized Loss by Length of Time (Details) $ in Millions	Sep. 30, 2023 USD ($) Security	Dec. 31, 2022 USD ($) Security
Less than 12 months
Fair Value	$ 2,093	$ 3,751
Gross Unrealized Loss	$ (58)	$ (213)
Number of securities | Security	795	1,340
12 months or more
Fair Value	$ 3,150	$ 1,017
Gross Unrealized Loss	$ (436)	$ (239)
Number of securities | Security	1,308	466
Total
Fair Value	$ 5,243	$ 4,768
Gross Unrealized Loss	$ (494)	$ (452)
Number of securities | Security	2,079	1,776
Obligations of state and political subdivisions
Less than 12 months
Fair Value	$ 1,610	$ 1,763
Gross Unrealized Loss	(39)	(79)
12 months or more
Fair Value	899	163
Gross Unrealized Loss	(136)	(56)
Total
Fair Value	2,509	1,926
Gross Unrealized Loss	(175)	(135)
U.S. government and agencies
Less than 12 months
Fair Value	21	32
Gross Unrealized Loss	0	0
12 months or more
Fair Value	32	52
Gross Unrealized Loss	(7)	(8)
Total
Fair Value	53	84
Gross Unrealized Loss	(7)	(8)
Corporate securities
Less than 12 months
Fair Value	381	1,276
Gross Unrealized Loss	(14)	(95)
12 months or more
Fair Value	1,396	519
Gross Unrealized Loss	(236)	(147)
Total
Fair Value	1,777	1,795
Gross Unrealized Loss	(250)	(242)
RMBS
Less than 12 months
Fair Value	55	147
Gross Unrealized Loss	(3)	(9)
12 months or more
Fair Value	122	3
Gross Unrealized Loss	(14)	(1)
Total
Fair Value	177	150
Gross Unrealized Loss	(17)	(10)
CMBS
Less than 12 months
Fair Value	3	270
Gross Unrealized Loss	0	(11)
12 months or more
Fair Value	184	0
Gross Unrealized Loss	(10)	0
Total
Fair Value	187	270
Gross Unrealized Loss	(10)	(11)
CLOs
Less than 12 months
Fair Value	18	171
Gross Unrealized Loss	(2)	(7)
12 months or more
Fair Value	402	250
Gross Unrealized Loss	(8)	(14)
Total
Fair Value	420	421
Gross Unrealized Loss	(10)	(21)
Other
Less than 12 months
Fair Value	1	27
Gross Unrealized Loss	0	(2)
12 months or more
Fair Value	26	0
Gross Unrealized Loss	(2)	0
Total
Fair Value	27	27
Gross Unrealized Loss	(2)	(2)
Non-U.S. government securities
Less than 12 months
Fair Value	4	65
Gross Unrealized Loss	0	(10)
12 months or more
Fair Value	89	30
Gross Unrealized Loss	(23)	(13)
Total
Fair Value	93	95
Gross Unrealized Loss	$ (23)	$ (23)

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