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	Mar. 31, 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	$ 21,577	$ 5,563
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,288)	(81)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	746	3,337
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(87)	(88)
Debt Securities, Available-for-sale, Unrealized Loss Position	22,323	8,900
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(1,375)	(169)
U.S. Treasury and 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)
Foreign
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	6,534	1,846
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(376)	(34)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	132	802
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(21)	(28)
Debt Securities, Available-for-sale, Unrealized Loss Position	6,666	2,648
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(397)	(62)
Corporate securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	13,492	2,121
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(858)	(40)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	448	988
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(51)	(40)
Debt Securities, Available-for-sale, Unrealized Loss Position	13,940	3,109
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(909)	(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	914	1,174
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(48)	(6)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	36	932
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(4)	(8)
Debt Securities, Available-for-sale, Unrealized Loss Position	950	2,106
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	(52)	(14)
States, municipalities, and political subdivisions
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	637	188
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(6)	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	130	276
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(11)	(12)
Debt Securities, Available-for-sale, Unrealized Loss Position	767	464
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (17)	$ (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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