Investments (Aggregate Fair Value And Gross Unrealized Loss By Length Of Time Security Has Continuously Been In Unrealized Loss Position) (Details) - USD ($) $ in Millions	Sep. 30, 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	$ 9,367	$ 27,956
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(166)	(518)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	34,783	39,789
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(3,048)	(4,230)
Debt Securities, Available-for-sale, Unrealized Loss Position	44,150	67,745
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(3,214)	(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	274	767
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2)	(16)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,195	2,489
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(222)	(303)
Debt Securities, Available-for-sale, Unrealized Loss Position	2,469	3,256
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(224)	(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	4,617	6,630
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(100)	(138)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	9,797	12,023
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(595)	(874)
Debt Securities, Available-for-sale, Unrealized Loss Position	14,414	18,653
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(695)	(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	3,551	10,069
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(57)	(194)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	11,096	13,290
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(928)	(1,259)
Debt Securities, Available-for-sale, Unrealized Loss Position	14,647	23,359
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(985)	(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	925	10,490
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(7)	(170)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	11,695	11,987
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,303)	(1,794)
Debt Securities, Available-for-sale, Unrealized Loss Position	12,620	22,477
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (1,310)	$ (1,964)