Investments (Aggregate Fair Value And Gross Unrealized Loss By Length Of Time Security Has Continuously Been In Unrealized Loss Position) (Detail) - Fixed Maturities [Member] - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 18,808	$ 4,755
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(339)	(75)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,607	758
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(65)	(22)
Debt Securities, Available-for-sale, Unrealized Loss Position	20,415	5,513
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(404)	(97)
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	231
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(5)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	231
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(5)
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	5,704	1,628
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(147)	(35)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	780	114
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(40)	(5)
Debt Securities, Available-for-sale, Unrealized Loss Position	6,484	1,742
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(187)	(40)
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	6,686	2,212
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(124)	(33)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	662	593
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(20)	(14)
Debt Securities, Available-for-sale, Unrealized Loss Position	7,348	2,805
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(144)	(47)
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	5,948	875
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(61)	(6)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	157	35
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(4)	(2)
Debt Securities, Available-for-sale, Unrealized Loss Position	6,105	910
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(65)	(8)
Municipal
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	239	40
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2)	(1)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	8	16
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	(1)
Debt Securities, Available-for-sale, Unrealized Loss Position	247	56
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (3)	$ (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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Amount of accumulated unrealized loss on 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 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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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 less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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