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, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 14,450	$ 8,569
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(242)	(176)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	52,582	53,950
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(4,784)	(4,129)
Debt Securities, Available-for-sale, Unrealized Loss Position	67,032	62,519
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(5,026)	(4,305)
U.S. Treasury / Agency
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	632	463
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(13)	(9)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,007	2,504
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(151)	(135)
Debt Securities, Available-for-sale, Unrealized Loss Position	2,639	2,967
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(164)	(144)
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	3,793	2,464
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(64)	(43)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	15,928	15,971
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,079)	(957)
Debt Securities, Available-for-sale, Unrealized Loss Position	19,721	18,435
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(1,143)	(1,000)
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	4,675	2,866
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(71)	(51)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	19,646	20,334
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,487)	(1,194)
Debt Securities, Available-for-sale, Unrealized Loss Position	24,321	23,200
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(1,558)	(1,245)
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	4,907	1,659
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(82)	(58)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	13,783	13,831
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,919)	(1,706)
Debt Securities, Available-for-sale, Unrealized Loss Position	18,690	15,490
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(2,001)	(1,764)
Municipal
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	443	1,117
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(12)	(15)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,218	1,310
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(148)	(137)
Debt Securities, Available-for-sale, Unrealized Loss Position	1,661	2,427
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (160)	$ (152)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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