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, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 10,668	$ 5,563
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(247)	(81)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	923	3,337
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(59)	(88)
Debt Securities, Available-for-sale, Unrealized Loss Position	11,591	8,900
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(306)	(169)
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		234
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		(1)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer		339
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Debt Securities, Available-for-sale, Unrealized Loss Position		573
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		(1)
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	2,848	1,846
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(89)	(34)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	122	802
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(14)	(28)
Debt Securities, Available-for-sale, Unrealized Loss Position	2,970	2,648
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(103)	(62)
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	6,149	2,121
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(145)	(40)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	721	988
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(41)	(40)
Debt Securities, Available-for-sale, Unrealized Loss Position	6,870	3,109
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(186)	(80)
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	1,481	1,174
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(11)	(6)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	26	932
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2)	(8)
Debt Securities, Available-for-sale, Unrealized Loss Position	1,507	2,106
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(13)	(14)
Municipal
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	190	188
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	54	276
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2)	(12)
Debt Securities, Available-for-sale, Unrealized Loss Position	244	464
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (4)	$ (12)

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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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