Investments (Aggregate Fair Value And Gross Unrealized Loss By Length Of Time Security Has Continuously Been In Unrealized Loss Position) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 21,870	$ 27,956
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(334)	(518)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	38,653	39,789
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(3,763)	(4,230)
Debt Securities, Available-for-sale, Unrealized Loss Position	60,523	67,745
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(4,097)	(4,748)
U.S. and local government securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	524	767
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(7)	(16)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,468	2,489
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(253)	(303)
Debt Securities, Available-for-sale, Unrealized Loss Position	2,992	3,256
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(260)	(319)
Non-U.S.
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	5,533	6,630
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(102)	(138)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	11,375	12,023
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(774)	(874)
Debt Securities, Available-for-sale, Unrealized Loss Position	16,908	18,653
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(876)	(1,012)
Corporate and asset-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	10,320	10,069
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(177)	(194)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	12,824	13,290
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,172)	(1,259)
Debt Securities, Available-for-sale, Unrealized Loss Position	23,144	23,359
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(1,349)	(1,453)
Mortgage-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	5,493	10,490
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(48)	(170)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	11,986	11,987
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,564)	(1,794)
Debt Securities, Available-for-sale, Unrealized Loss Position	17,479	22,477
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (1,612)	$ (1,964)