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, 2019	Dec. 31, 2018
Investment [Line Items]
Fair Value 0-12 months	$ 5,111	$ 34,952
Gross unrealized (loss) 0-12 months	(88)	(953)
Fair Value over 12 months	4,239	27,762
Gross unrealized (loss) over 12 months	(120)	(817)
Fair Value	9,350	62,714
Gross unrealized (loss)	(208)	(1,770)
U.S. Treasury and agency
Investment [Line Items]
Fair Value 0-12 months	144	523
Gross unrealized (loss) 0-12 months	0	(4)
Fair Value over 12 months	531	2,859
Gross unrealized (loss) over 12 months	(1)	(50)
Fair Value	675	3,382
Gross unrealized (loss)	(1)	(54)
Foreign
Investment [Line Items]
Fair Value 0-12 months	1,077	6,764
Gross unrealized (loss) 0-12 months	(23)	(208)
Fair Value over 12 months	1,014	5,349
Gross unrealized (loss) over 12 months	(46)	(159)
Fair Value	2,091	12,113
Gross unrealized (loss)	(69)	(367)
Corporate securities
Investment [Line Items]
Fair Value 0-12 months	2,600	16,538
Gross unrealized (loss) 0-12 months	(62)	(599)
Fair Value over 12 months	1,095	4,873
Gross unrealized (loss) over 12 months	(50)	(255)
Fair Value	3,695	21,411
Gross unrealized (loss)	(112)	(854)
Mortgage-backed securities
Investment [Line Items]
Fair Value 0-12 months	640	6,103
Gross unrealized (loss) 0-12 months	(2)	(98)
Fair Value over 12 months	1,228	6,913
Gross unrealized (loss) over 12 months	(11)	(229)
Fair Value	1,868	13,016
Gross unrealized (loss)	(13)	(327)
States, municipalities, and political subdivisions
Investment [Line Items]
Fair Value 0-12 months	650	5,024
Gross unrealized (loss) 0-12 months	(1)	(44)
Fair Value over 12 months	371	7,768
Gross unrealized (loss) over 12 months	(12)	(124)
Fair Value	1,021	12,792
Gross unrealized (loss)	$ (13)	$ (168)