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, 2019	Dec. 31, 2018
Investment [Line Items]
Fair Value 0-12 months	$ 5,544	$ 34,952
Gross unrealized (loss) 0-12 months	(89)	(953)
Fair Value over 12 months	26,573	27,762
Gross unrealized (loss) over 12 months	(406)	(817)
Fair Value	32,117	62,714
Gross unrealized (loss)	(495)	(1,770)
U.S. Treasury and agency
Investment [Line Items]
Fair Value 0-12 months	68	523
Gross unrealized (loss) 0-12 months	0	(4)
Fair Value over 12 months	2,298	2,859
Gross unrealized (loss) over 12 months	(22)	(50)
Fair Value	2,366	3,382
Gross unrealized (loss)	(22)	(54)
Foreign
Investment [Line Items]
Fair Value 0-12 months	1,346	6,764
Gross unrealized (loss) 0-12 months	(26)	(208)
Fair Value over 12 months	4,228	5,349
Gross unrealized (loss) over 12 months	(89)	(159)
Fair Value	5,574	12,113
Gross unrealized (loss)	(115)	(367)
Corporate securities
Investment [Line Items]
Fair Value 0-12 months	3,649	16,538
Gross unrealized (loss) 0-12 months	(62)	(599)
Fair Value over 12 months	6,206	4,873
Gross unrealized (loss) over 12 months	(142)	(255)
Fair Value	9,855	21,411
Gross unrealized (loss)	(204)	(854)
Mortgage-backed securities
Investment [Line Items]
Fair Value 0-12 months	388	6,103
Gross unrealized (loss) 0-12 months	(1)	(98)
Fair Value over 12 months	8,974	6,913
Gross unrealized (loss) over 12 months	(117)	(229)
Fair Value	9,362	13,016
Gross unrealized (loss)	(118)	(327)
States, municipalities, and political subdivisions
Investment [Line Items]
Fair Value 0-12 months	93	5,024
Gross unrealized (loss) 0-12 months	0	(44)
Fair Value over 12 months	4,867	7,768
Gross unrealized (loss) over 12 months	(36)	(124)
Fair Value	4,960	12,792
Gross unrealized (loss)	$ (36)	$ (168)