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Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	$ 8,825	$ 3,867
Estimated Fair Value - 12 Months or More	8,329	9,555
Estimated Fair Value	17,154	13,422
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(105)	(67)
Gross Unrealized Losses - 12 Months or More	(723)	(760)
Gross Unrealized Losses	(828)	(827)
Fixed maturities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	8,098	3,565
Estimated Fair Value - 12 Months or More	8,329	9,555
Estimated Fair Value	16,427	13,120
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(102)	(65)
Gross Unrealized Losses - 12 Months or More	(723)	(760)
Gross Unrealized Losses	(825)	(825)
Corporate bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	3,314	1,559
Estimated Fair Value - 12 Months or More	4,419	4,959
Estimated Fair Value	7,733	6,518
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(50)	(45)
Gross Unrealized Losses - 12 Months or More	(392)	(419)
Gross Unrealized Losses	(442)	(464)
U.S. government and government agencies
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	3,093	1,066
Estimated Fair Value - 12 Months or More	763	941
Estimated Fair Value	3,856	2,007
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(36)	(10)
Gross Unrealized Losses - 12 Months or More	(73)	(76)
Gross Unrealized Losses	(109)	(86)
Non-U.S. government securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	829	365
Estimated Fair Value - 12 Months or More	821	897
Estimated Fair Value	1,650	1,262
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(10)	(4)
Gross Unrealized Losses - 12 Months or More	(103)	(96)
Gross Unrealized Losses	(113)	(100)
Residential mortgage backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	267	221
Estimated Fair Value - 12 Months or More	508	522
Estimated Fair Value	775	743
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(4)	(3)
Gross Unrealized Losses - 12 Months or More	(65)	(63)
Gross Unrealized Losses	(69)	(66)
Asset backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	489	234
Estimated Fair Value - 12 Months or More	729	1,112
Estimated Fair Value	1,218	1,346
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(1)	(1)
Gross Unrealized Losses - 12 Months or More	(43)	(54)
Gross Unrealized Losses	(44)	(55)
Commercial mortgage backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	88	100
Estimated Fair Value - 12 Months or More	892	909
Estimated Fair Value	980	1,009
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(1)	(1)
Gross Unrealized Losses - 12 Months or More	(29)	(33)
Gross Unrealized Losses	(30)	(34)
Municipal bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	18	20
Estimated Fair Value - 12 Months or More	197	215
Estimated Fair Value	215	235
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	0	(1)
Gross Unrealized Losses - 12 Months or More	(18)	(19)
Gross Unrealized Losses	(18)	(20)
Short-term investments
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	727	302
Estimated Fair Value - 12 Months or More	0	0
Estimated Fair Value	727	302
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(3)	(2)
Gross Unrealized Losses - 12 Months or More	0	0
Gross Unrealized Losses	$ (3)	$ (2)

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