Investments (Aggregate Fair Value And Gross Unrealized Loss By Length Of Time Security Has Continuously Been In Unrealized Loss Position) (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Investment [Line Items]
Fair Value, 0-12 Months	$ 7,376	$ 16,763
Gross Unrealized Loss, 0-12 Months	(141)	(601)
Fair Value, Over 12 Months	2,194	1,885
Gross Unrealized Loss, Over 12 Months	(115)	(226)
Total Fair Value	9,570	18,648
Total Gross Unrealized Loss	(256)	(827)
U.S. Treasury And Agency [Member]
Investment [Line Items]
Fair Value, 0-12 Months		996
Gross Unrealized Loss, 0-12 Months		(5)
Fair Value, Over 12 Months		153
Gross Unrealized Loss, Over 12 Months		(1)
Total Fair Value		1,149
Total Gross Unrealized Loss		(6)
Foreign [Member]
Investment [Line Items]
Fair Value, 0-12 Months	2,266	3,953
Gross Unrealized Loss, 0-12 Months	(27)	(148)
Fair Value, Over 12 Months	673	436
Gross Unrealized Loss, Over 12 Months	(43)	(73)
Total Fair Value	2,939	4,389
Total Gross Unrealized Loss	(70)	(221)
Corporate [Member]
Investment [Line Items]
Fair Value, 0-12 Months	2,855	7,518
Gross Unrealized Loss, 0-12 Months	(61)	(371)
Fair Value, Over 12 Months	1,047	738
Gross Unrealized Loss, Over 12 Months	(68)	(138)
Total Fair Value	3,902	8,256
Total Gross Unrealized Loss	(129)	(509)
Collateralized Mortgage Backed Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	481	3,399
Gross Unrealized Loss, 0-12 Months	(3)	(42)
Fair Value, Over 12 Months	414	516
Gross Unrealized Loss, Over 12 Months	(3)	(12)
Total Fair Value	895	3,915
Total Gross Unrealized Loss	(6)	(54)
States, Municipalities, And Political Subdivisions [Member]
Investment [Line Items]
Fair Value, 0-12 Months	1,308	556
Gross Unrealized Loss, 0-12 Months	(4)	(6)
Fair Value, Over 12 Months	60	42
Gross Unrealized Loss, Over 12 Months	(1)	(2)
Total Fair Value	1,368	598
Total Gross Unrealized Loss	(5)	(8)
Fixed Maturities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	6,910	16,422
Gross Unrealized Loss, 0-12 Months	(95)	(572)
Fair Value, Over 12 Months	2,194	1,885
Gross Unrealized Loss, Over 12 Months	(115)	(226)
Total Fair Value	9,104	18,307
Total Gross Unrealized Loss	(210)	(798)
Equity Securities [Member]
Investment [Line Items]
Fair Value, 0-12 Months	186	131
Gross Unrealized Loss, 0-12 Months	(19)	(18)
Fair Value, Over 12 Months	0	0
Gross Unrealized Loss, Over 12 Months	0	0
Total Fair Value	186	131
Total Gross Unrealized Loss	(19)	(18)
Other Long-term Investments [Member]
Investment [Line Items]
Fair Value, 0-12 Months	280	210
Gross Unrealized Loss, 0-12 Months	(27)	(11)
Fair Value, Over 12 Months	0	0
Gross Unrealized Loss, Over 12 Months	0	0
Total Fair Value	280	210
Total Gross Unrealized Loss	$ (27)	$ (11)