Investment Information - Aging of available for sale securities in an unrealized loss position (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	$ 9,849	$ 12,494
Estimated Fair Value - 12 Months or More	4,356	5,080
Estimated Fair Value	14,205	17,574
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(155)	(290)
Gross Unrealized Losses - 12 Months or More	(320)	(404)
Gross Unrealized Losses	(475)	(694)
Fixed maturities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	9,028	12,397
Estimated Fair Value - 12 Months or More	4,356	5,080
Estimated Fair Value	13,384	17,477
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(154)	(288)
Gross Unrealized Losses - 12 Months or More	(320)	(404)
Gross Unrealized Losses	(474)	(692)
Corporate bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	3,812	4,582
Estimated Fair Value - 12 Months or More	2,569	2,924
Estimated Fair Value	6,381	7,506
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(84)	(114)
Gross Unrealized Losses - 12 Months or More	(183)	(232)
Gross Unrealized Losses	(267)	(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	2,160	5,130
Estimated Fair Value - 12 Months or More	403	516
Estimated Fair Value	2,563	5,646
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(25)	(100)
Gross Unrealized Losses - 12 Months or More	(28)	(49)
Gross Unrealized Losses	(53)	(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	1,387	1,650
Estimated Fair Value - 12 Months or More	411	418
Estimated Fair Value	1,798	2,068
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(33)	(58)
Gross Unrealized Losses - 12 Months or More	(48)	(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	269	571
Estimated Fair Value - 12 Months or More	180	186
Estimated Fair Value	449	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	(24)	(25)
Gross Unrealized Losses	(26)	(31)
Asset backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	1,016	236
Estimated Fair Value - 12 Months or More	396	426
Estimated Fair Value	1,412	662
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(7)	(8)
Gross Unrealized Losses - 12 Months or More	(23)	(24)
Gross Unrealized Losses	(30)	(32)
Commercial mortgage backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	367	180
Estimated Fair Value - 12 Months or More	238	434
Estimated Fair Value	605	614
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Gross Unrealized Losses - Less than 12 Months	(2)	(1)
Gross Unrealized Losses - 12 Months or More	(7)	(10)
Gross Unrealized Losses	(9)	(11)
Municipal bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	17	48
Estimated Fair Value - 12 Months or More	159	176
Estimated Fair Value	176	224
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	(7)	(15)
Gross Unrealized Losses	(8)	(16)
Short-term investments
Debt Securities, Available-for-sale, Unrealized Loss Position, Estimated Fair Value [Abstract]
Estimated Fair Value - Less than 12 Months	821	97
Estimated Fair Value - 12 Months or More	0	0
Estimated Fair Value	821	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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