Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Available for sale securities:
Estimated Fair Value - Less than 12 Months	$ 3,867	$ 12,976
Gross Unrealized Losses - Less than 12 Months	(67)	(929)
Estimated Fair Value - 12 Months or More	9,555	5,671
Gross Unrealized Losses - 12 Months or More	(760)	(720)
Estimated Fair Value - Total	13,422	18,647
Gross Unrealized Losses - Total	(827)	(1,649)
Fixed maturities available for sale, at fair value
Available for sale securities:
Estimated Fair Value - Less than 12 Months	3,565	12,739
Gross Unrealized Losses - Less than 12 Months	(65)	(927)
Estimated Fair Value - 12 Months or More	9,555	5,671
Gross Unrealized Losses - 12 Months or More	(760)	(720)
Estimated Fair Value - Total	13,120	18,410
Gross Unrealized Losses - Total	(825)	(1,647)
Corporate bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	1,559	4,823
Gross Unrealized Losses - Less than 12 Months	(45)	(393)
Estimated Fair Value - 12 Months or More	4,959	2,559
Gross Unrealized Losses - 12 Months or More	(419)	(388)
Estimated Fair Value - Total	6,518	7,382
Gross Unrealized Losses - Total	(464)	(781)
US government and government agencies
Available for sale securities:
Estimated Fair Value - Less than 12 Months	1,066	3,557
Gross Unrealized Losses - Less than 12 Months	(10)	(197)
Estimated Fair Value - 12 Months or More	941	1,443
Gross Unrealized Losses - 12 Months or More	(76)	(146)
Estimated Fair Value - Total	2,007	5,000
Gross Unrealized Losses - Total	(86)	(343)
Non-US government securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	365	1,703
Gross Unrealized Losses - Less than 12 Months	(4)	(154)
Estimated Fair Value - 12 Months or More	897	542
Gross Unrealized Losses - 12 Months or More	(96)	(84)
Estimated Fair Value - Total	1,262	2,245
Gross Unrealized Losses - Total	(100)	(238)
Mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	221	546
Gross Unrealized Losses - Less than 12 Months	(3)	(52)
Estimated Fair Value - 12 Months or More	522	154
Gross Unrealized Losses - 12 Months or More	(63)	(35)
Estimated Fair Value - Total	743	700
Gross Unrealized Losses - Total	(66)	(87)
Asset backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	234	1,148
Gross Unrealized Losses - Less than 12 Months	(1)	(66)
Estimated Fair Value - 12 Months or More	1,112	512
Gross Unrealized Losses - 12 Months or More	(54)	(41)
Estimated Fair Value - Total	1,346	1,660
Gross Unrealized Losses - Total	(55)	(107)
Commercial mortgage backed securities
Available for sale securities:
Estimated Fair Value - Less than 12 Months	100	598
Gross Unrealized Losses - Less than 12 Months	(1)	(35)
Estimated Fair Value - 12 Months or More	909	445
Gross Unrealized Losses - 12 Months or More	(33)	(23)
Estimated Fair Value - Total	1,009	1,043
Gross Unrealized Losses - Total	(34)	(58)
Municipal bonds
Available for sale securities:
Estimated Fair Value - Less than 12 Months	20	364
Gross Unrealized Losses - Less than 12 Months	(1)	(30)
Estimated Fair Value - 12 Months or More	215	16
Gross Unrealized Losses - 12 Months or More	(19)	(3)
Estimated Fair Value - Total	235	380
Gross Unrealized Losses - Total	(20)	(33)
Short-term investments
Available for sale securities:
Estimated Fair Value - Less than 12 Months	302	237
Gross Unrealized Losses - Less than 12 Months	(2)	(2)
Estimated Fair Value - 12 Months or More	0	0
Gross Unrealized Losses - 12 Months or More	0	0
Estimated Fair Value - Total	302	237
Gross Unrealized Losses - Total	$ (2)	$ (2)

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