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	Jun. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Fair Value 0-12 months	$ 3,954	$ 34,952
Gross unrealized (loss) 0-12 months	(64)	(953)
Fair Value over 12 months	8,958	27,762
Gross unrealized (loss) over 12 months	(162)	(817)
Fair Value	12,912	62,714
Gross unrealized (loss)	(226)	(1,770)
U.S. Treasury and agency
Investment [Line Items]
Fair Value 0-12 months	41	523
Gross unrealized (loss) 0-12 months	0	(4)
Fair Value over 12 months	836	2,859
Gross unrealized (loss) over 12 months	(3)	(50)
Fair Value	877	3,382
Gross unrealized (loss)	(3)	(54)
Foreign
Investment [Line Items]
Fair Value 0-12 months	946	6,764
Gross unrealized (loss) 0-12 months	(14)	(208)
Fair Value over 12 months	2,042	5,349
Gross unrealized (loss) over 12 months	(58)	(159)
Fair Value	2,988	12,113
Gross unrealized (loss)	(72)	(367)
Corporate securities
Investment [Line Items]
Fair Value 0-12 months	2,617	16,538
Gross unrealized (loss) 0-12 months	(49)	(599)
Fair Value over 12 months	1,834	4,873
Gross unrealized (loss) over 12 months	(57)	(255)
Fair Value	4,451	21,411
Gross unrealized (loss)	(106)	(854)
Mortgage-backed securities
Investment [Line Items]
Fair Value 0-12 months	289	6,103
Gross unrealized (loss) 0-12 months	(1)	(98)
Fair Value over 12 months	2,779	6,913
Gross unrealized (loss) over 12 months	(28)	(229)
Fair Value	3,068	13,016
Gross unrealized (loss)	(29)	(327)
States, municipalities, and political subdivisions
Investment [Line Items]
Fair Value 0-12 months	61	5,024
Gross unrealized (loss) 0-12 months	0	(44)
Fair Value over 12 months	1,467	7,768
Gross unrealized (loss) over 12 months	(16)	(124)
Fair Value	1,528	12,792
Gross unrealized (loss)	$ (16)	$ (168)