Investment Information - Aging of available for sale securities in an unrealized loss position (Details) $ in Millions	Dec. 31, 2024 USD ($) lots	Dec. 31, 2023 USD ($) lots
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	$ 12,494	$ 3,867
Estimated Fair Value - 12 Months or More	5,080	9,555
Estimated Fair Value - Total	17,574	13,422
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(290)	(67)
Gross Unrealized Losses - 12 Months or More	(404)	(760)
Gross Unrealized Losses - Total	$ (694)	$ (827)
Continuous unrealized loss, qualitative disclosures:
Number of positions in an unrealized loss position (lots) | lots	9,980	7,100
Total number of positions (lots) | lots	20,930	15,720
Largest single loss	$ 8	$ 6
Fixed maturities available for sale, at fair value
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	12,397	3,565
Estimated Fair Value - 12 Months or More	5,080	9,555
Estimated Fair Value - Total	17,477	13,120
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(288)	(65)
Gross Unrealized Losses - 12 Months or More	(404)	(760)
Gross Unrealized Losses - Total	(692)	(825)
Corporate bonds
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	4,582	1,559
Estimated Fair Value - 12 Months or More	2,924	4,959
Estimated Fair Value - Total	7,506	6,518
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(114)	(45)
Gross Unrealized Losses - 12 Months or More	(232)	(419)
Gross Unrealized Losses - Total	(346)	(464)
US government and government agencies
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	5,130	1,066
Estimated Fair Value - 12 Months or More	516	941
Estimated Fair Value - Total	5,646	2,007
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(100)	(10)
Gross Unrealized Losses - 12 Months or More	(49)	(76)
Gross Unrealized Losses - Total	(149)	(86)
Non-US government securities
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	1,650	365
Estimated Fair Value - 12 Months or More	418	897
Estimated Fair Value - Total	2,068	1,262
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(58)	(4)
Gross Unrealized Losses - 12 Months or More	(49)	(96)
Gross Unrealized Losses - Total	(107)	(100)
Mortgage backed securities
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	571	221
Estimated Fair Value - 12 Months or More	186	522
Estimated Fair Value - Total	757	743
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(6)	(3)
Gross Unrealized Losses - 12 Months or More	(25)	(63)
Gross Unrealized Losses - Total	(31)	(66)
Asset backed securities
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	236	234
Estimated Fair Value - 12 Months or More	426	1,112
Estimated Fair Value - Total	662	1,346
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(8)	(1)
Gross Unrealized Losses - 12 Months or More	(24)	(54)
Gross Unrealized Losses - Total	(32)	(55)
Commercial mortgage backed securities
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	180	100
Estimated Fair Value - 12 Months or More	434	909
Estimated Fair Value - Total	614	1,009
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(1)	(1)
Gross Unrealized Losses - 12 Months or More	(10)	(33)
Gross Unrealized Losses - Total	(11)	(34)
Municipal bonds
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	48	20
Estimated Fair Value - 12 Months or More	176	215
Estimated Fair Value - Total	224	235
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(1)	(1)
Gross Unrealized Losses - 12 Months or More	(15)	(19)
Gross Unrealized Losses - Total	(16)	(20)
Short-term investments
Estimated Fair Value
Estimated Fair Value - Less than 12 Months	97	302
Estimated Fair Value - 12 Months or More	0	0
Estimated Fair Value - Total	97	302
Gross Unrealized Losses
Gross Unrealized Losses - Less than 12 Months	(2)	(2)
Gross Unrealized Losses - 12 Months or More	0	0
Gross Unrealized Losses - Total	$ (2)	$ (2)