Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	$ 8,984	$ 12,494
Estimated Fair Value - 12 Months or More	3,153	5,080
Estimated Fair Value	12,137	17,574
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(133)	(290)
Gross Unrealized Losses - 12 Months or More	(205)	(404)
Gross Unrealized Losses	(338)	(694)
Fixed maturities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	8,368	12,397
Estimated Fair Value - 12 Months or More	3,153	5,080
Estimated Fair Value	11,521	17,477
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(132)	(288)
Gross Unrealized Losses - 12 Months or More	(205)	(404)
Gross Unrealized Losses	(337)	(692)
Corporate bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	2,489	4,582
Estimated Fair Value - 12 Months or More	1,714	2,924
Estimated Fair Value	4,203	7,506
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(73)	(114)
Gross Unrealized Losses - 12 Months or More	(100)	(232)
Gross Unrealized Losses	(173)	(346)
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	3,205	5,130
Estimated Fair Value - 12 Months or More	359	516
Estimated Fair Value	3,564	5,646
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(18)	(100)
Gross Unrealized Losses - 12 Months or More	(13)	(49)
Gross Unrealized Losses	(31)	(149)
Non-U.S. government securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	1,671	1,650
Estimated Fair Value - 12 Months or More	343	418
Estimated Fair Value	2,014	2,068
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(36)	(58)
Gross Unrealized Losses - 12 Months or More	(45)	(49)
Gross Unrealized Losses	(81)	(107)
Residential mortgage backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	193	571
Estimated Fair Value - 12 Months or More	168	186
Estimated Fair Value	361	757
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(2)	(6)
Gross Unrealized Losses - 12 Months or More	(20)	(25)
Gross Unrealized Losses	(22)	(31)
Asset backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	461	236
Estimated Fair Value - 12 Months or More	339	426
Estimated Fair Value	800	662
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(2)	(8)
Gross Unrealized Losses - 12 Months or More	(17)	(24)
Gross Unrealized Losses	(19)	(32)
Commercial mortgage backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	336	180
Estimated Fair Value - 12 Months or More	84	434
Estimated Fair Value	420	614
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	(5)	(10)
Gross Unrealized Losses	(6)	(11)
Municipal bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	13	48
Estimated Fair Value - 12 Months or More	146	176
Estimated Fair Value	159	224
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	(5)	(15)
Gross Unrealized Losses	(5)	(16)
Short-term investments
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	616	97
Estimated Fair Value - 12 Months or More	0	0
Estimated Fair Value	616	97
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(1)	(2)
Gross Unrealized Losses - 12 Months or More	0	0
Gross Unrealized Losses	$ (1)	$ (2)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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